Chapter XXIV: Summary and Conclusion (2)

I.
Ice-action, what evidences of, during the Tertiary period, 178
indications of ancient, 200
Ice-borne rocks, a test of a glacial epoch, 176
in Miocene of N. Italy, 178
in Eocene of Alps, 178
in Eocene of Carpathians and Apennines, 179
absence of, in English and N. American Tertiaries, 180
Ice-cap, why improbable or impossible, 161
Iceland, a continental island, 450
Icteridae, 50
Iguanidae, 50
Indian birds in Formosa, 407
Indian Ocean as a source of heat in Tertiary times, 192
Indian genera of plants in Australia, 492
Indicator, distribution of, 25
Insectivora in Madagascar, 417
Insects, dispersal of, 77
of the Miocene period, 77
restriction of range of, 78
of the Azores, 253
of Bermuda, 269
of the Galapagos, 284
of St. Helena, 298
of the Sandwich Islands, 318
peculiar British, 344
of Celebes, peculiarities of, 462
scarcity of, in New Zealand, 505
Insular faunas, summary of conclusions as to, 539, 542
Interglacial warm periods on the continent and in North America, 121
Interglacial periods and their probable character, 152
Interglacial periods will not occur during an epoch of extreme
glaciation, 155
Interglacial climates never very warm, 159
Ireland, poverty of, in reptiles, 339
in plants, 339
peculiar fishes of, 342
plants of, not found in Great Britain, 364
Islands, classification of, 242
importance of, in study of distribution, 241
remote, how stocked with plants and animals, 261
submerged between Madagascar and India, 425
Isle of Wight, peculiar beetle of, 351
_Isatis tinctoria_, on railway bank, 513
Ithaginis, 26

J.
Japan, zoological features of, 393
mammalia of, 394
birds of, 396
birds peculiar to, 398
birds in distant areas, 399
Japan and Formosa, 391
Java, fauna of, 382
Asiatic species in, 384
Java and Borneo, past changes of, 385
Jays, distribution of species of, 20
of Europe and Japan, 67
Jeffreys, Dr. Gwyn, on shallow-water mollusca in chalk, 92
on fossil shallow-water shells in deep water, 337
Jones, Mr., on migration of birds to Bermuda, 268
on vegetation of the Bermudas, 272
Juan Fernandez, flora and fauna of, 287
Judd, Prof. J. W., on absence of glaciation in east Europe, 139
on glaciation of the Alps produced by elevation, 179
_Juniperus barbadensis_, 272
Jura, travelled blocks on, 110
Jurassic warm Arctic climate, 202

K.
Keeling Islands, animals of, 286
Kirk, Mr. T., on temporary introduced plants, 515
Knowledge of various kinds required for study of geographical
distribution, 7, 9

L.
_Lagopus scoticus_, 340
Land as a barrier to ocean-currents, 150
{557}
Land and sea, changes of, 83
how changes of, affect climate, 148, 150
Land and water, disproportion of, renders globe habitable, 209
Land-birds of Celebes, list of, 466
Land-connection, how far necessary to dispersal of mammals, 73
Land-shells, great antiquity of, 79
universal distribution of, 79
causes favouring the abundance of, 79
of the Azores, 256
of Bermuda, 270
of the Galapagos, 284
of St. Helena, 304
of the Sandwich Islands, 316
of the Seychelles, 434
_Laurus canariensis_, 260
Leguat on animals of Bourbon, 435
on the Solitaire, 436
Leguminosae, abundance of, in Australia, 490
"Lemuria," a supposed submerged continent, 422-426
Lemurs in Madagascar, 416
Lendenfeld, Dr. R. von, on glaciation in the Australian Alps, 163
Leopard, enormous range of, 14
Lepidoptera, list of peculiar British, 347
Lepidosiren, 63
_Lepidosiren paradoxa_ and _L. annectens_, 69
Lepidosternidae, 27
Limestone as indicating change of sea and land, 84
_Limnaea involuta_, 356
_Linaria purpurea_, on railway bank, 514
_Liopelma hochstetteri_, in New Zealand, 483
Liotrichidae, 29
List of the land-birds of Celebes, 466
Lizard peculiar to the Mascarene Islands, 438
Lizards of the Galapagos, 278
local variation of colour of, 431
of New Zealand, 483
Lobeliaceae, abundance of, in the Sandwich Islands, 324
Locality of a species, importance of, 12
_Loddigesia mirabilis_, rarity of, 16
Lord, Mr., on species of Urotrichus, 394
Low-grade and high-grade heat, 145
Lowlands nowhere covered with perpetual snow, 136
Lundy Island, peculiar beetles of, 354
Lyell, Sir Charles, on permanence of continents, 84
on calcareous mud, 90
on the distribution of chalk, 93
on geographical causes as modifying climate, 148
on estimate of geological time, 211, 235
on classification of sedimentary rocks, 217
Lynxes, a Palaearctic group, 41

M.
McLachlan, Mr., on peculiar British caddis-flies, 355
Madagascar, physical features of, 412
former condition of, 414
biological features of, 416
mammalia of, 416
reptiles of, 417
relation of, to Africa, 418
early history of, 419
birds of, in relation to "Lemuria," 422
flora of, 439
conclusion on fauna and flora of, 446
great antiquity of, 446
Madagascar and Africa, contrast of, 6
Maillard on animals of Bourbon, 435
Malay Islands, local peculiarities of flora in, 187
past history of, 389
Malayan birds in Formosa, 406
Mammalia of East Asia, range of, 34
of North Africa, range of, 34
Mammalia, dispersal of, 73
of Britain, range of, 33
poverty of, 329
of Borneo, 376
of Java, 382
of the Philippines, 387
of Japan, 393
of Formosa, 402
common to Formosa and India, 403
of Madagascar, 416
of Comoro Islands, 428
of Celebes, 455; whence derived, 457
of New Zealand, 474
Maori legend of origin of the forest-rat, 475
Maoris, their accounts of the moa, 477
Map of the old Rhone glacier, 110
of North and South Polar Regions, 138
of the Azores, 248
of Bermuda, 263
of the Galapagos, 276, 277
of the South Atlantic Ocean, 293
of the Sandwich Islands, 311
of the North Pacific with its submerged banks, 312
of British Isles and the 100-fathom bank, 333
of Borneo and Java, 374
of Japan and Formosa, 392
physical, of Madagascar, 413
of the Madagascar group, 415
of the Indian Ocean, 425
of Celebes, 452
of sea-bottom around New Zealand, 472
of Australia in Cretaceous period, 497
Marcou, Professor Jules, on the Pliocene and glacial epochs, 233
Marmot, range of, 15
Mars as illustrating glacial theories, 164, 168
{558}
Mars, no true ice-cap on, 166
Marsupials, range of, 30
Marsh, Prof. O. C., on the Atlantosaurus, 98
on Hesperornis, 481
Marsh, Mr., on camels as desert-makers, 296
Mascarene Islands, 428-445
Mascarene plants, curious relations of, 442
endemic genera of, 443
Mascarene flora, fragmentary character of, 444
abundance of ferns in, 445
Mauritius, Bourbon, and Rodriguez, 434
Measurements of geological time, 233
agreement of various estimates of, 235
concluding remarks on, 236
_Medicago sativa_ in New Zealand, 515
Megalaemidae, 27
Meleagris, 50
_Melilotus vulgaris_, on railway banks, 513
Meliphagidae, 47
Melliss, Mr., on the early history of St. Helena, 295
_Melospiza melodia_, variation of, 58
Merycotherium, 123
Meteorological causes as intensifying glaciation, 142
Migration caused by glacial epoch, 122
of birds to Bermuda, 267
of plants from north to south, 512
of plants and alterations of snow line, 516
of plants due to changes of climate, 517
of plants from north to south, long continued, 518
of plants aided by geological changes, 519
of plants by way of the Andes, 520
of plants by way of Himalayas and South Asia, 523
of plants through Africa, 524
Mild Arctic climates, stratigraphical evidence of, 187
causes of, 190
dependent on geographical changes, 191
effects of high excentricity on, 198
summary of causes of, 537
Miocene Arctic flora, 183
flora of Europe, 123
or Eocene floras, 185
deposits of Java, 385
fauna of Europe and North India, 419
Mississippi, matter carried away by, 172
Mitten, Mr. William, on peculiar British mosses and hepaticae, 365, 368
on temporary appearance of plants, 513
Mniotiltidae, a nearctic group, 49
Mnium, peculiar species of, in the Drontheim mountains, 368
Moas of New Zealand, 476
Mollusca, dispersal of, 78
Monotremata, restricted range of, 30
Moraines, 108
of Ivrea, 116
More, Mr. A. G., on peculiar Irish plants, 364
Morgan, Mr. C. Lloyd, on thickness of formations not affected by
denudation, 220
Moseley, Mr. H. N., on seeds carried by birds, 259
on the flora of Bermuda, 272
Mosses, peculiar British, 366
non-European genera of, in Britain, 367
how diffused and why restricted, 368
Mt. St. Elias, why not ice-clad, 154
Mountain chains aiding the dispersal of plants, 81
as aids to migration of plants, 513
Mueller, Baron von, census of Australian plants, 492
_Munia brunneiceps_, in Celebes, 463
Murray, Mr. J., on oceanic deposits, 86
on chalk-like globigerina-ooze, 92
on mean height of continents, 216
on land-area of the globe, 221
Mus, 17, 26
_Mygale pyrenaica_, range of, 15, 24
_M. muscovitica_, 24
_Myialestes helianthea_ in Celebes, 463
_Myrica faya_, 260
Myrsine, fossil in Greenland, 186
_Mytilus edulis_, sub-fossil in Spitzbergen, 182

N.
Nares, Capt. Sir G., on snow and ice in high latitudes, 135
on abrupt elevation of Bermuda, 264
Nearctic Region, definition of, 48
mammalia of, 48
birds of, 49
reptiles of, 50
_Nectarinea osea_, restricted range of, 16
Neilgherries, Australian plants naturalized in, 528
Neotropical Region, definition of, 51
low types of, 52
Nevill, Mr. Geoffrey, on land-shells of the Seychelles, 434
on destruction of Seychelles flora, 445
New species, origin of, 56
Newton, Mr. E., on short wings of the Seychelles dove, 437
Newton, Professor, on recently extinct birds, 437
Newts, restricted range of, 30
New Zealand, recent glaciation of, 163
New Zealand, 471
geology of, 472
form of sea-bottom around, 473
zoological character of, 473
mammalia of, 474
{559}
wingless birds of, 476
past changes of, 478
winged birds and lower vertebrates of, 482
deductions from peculiarities of fauna of, 484
period of its union with N. Australia, 484
the flora of, 487, 506
origin of Australian element in the flora of, 498
tropical character of flora, 500
tropical genera common to Australia, 501
temperate species common to Australia, 502
route of Arctic plants to, 521
European plants in, 509
endemic genera of plants in, 526
great antiquity of, 526
Nordenskjoeld, Prof., on absence of perpetual snow in N. Asia, 135
on recent milder climate in Spitzbergen, 182
on former Polar climates, 187
on geology of Spitzbergen, 188
North America, glacial phenomena in, 116
interglacial warm periods in, 121
condition of, in Tertiary period, 194
Northern genera of plants in S. temperate America, 521
hemisphere, absence of southern plants from, 527
flora, hardiness of, 528

O.
Ocean-currents as carriers of plants, 81
as affecting interglacial periods, 152
as determining climate, 153
effects of, in Tertiary times, 196
Ocean, Darwin on permanence of, 100
Oceanic and continental islands, 242
Oceanic islands a proof of the permanence of oceans, 100
Oceanic islands, 244
--the Azores, 247
general remarks on, 329
Octodontidae, 27
_Oenanthe fluviatilis_, 361
Oeninghen, Miocene flora of, 183
_Oenothera odorata_, on a railway bank, 514
Oliver, Professor, on peculiar Bermudan plants, 272
Operculata, scarcity of, in the Sandwich Islands, 317
_Ophrys apifera_, temporary appearance of, 514
Orchideae, species have restricted ranges, 505
Orchids, abundance of, in Bourbon and Mauritius, 446
why almost universal in the tropics, 446
Orders, distribution of, 30
Organic change dependent on change of conditions, 225, 228
Oriental Region, definition of, 44
mammals and birds of, 44
reptiles of, 45
insects of, 45
Origin of new species, 56, 60
of new genera, 61
of the Galapagos flora, 288
of the beetles of St. Helena, 298
of Australian element in the New Zealand flora, 498
Orkney, peculiar fishes of, 341
Orthonyx not a New Zealand genus, 483
Osprey, wide range of, 15
Ostriches, limitation of, 30
Otter-like mammal in New Zealand, 475
Overlapping and discontinuous areas, 28

P.
_Pachyglossa aureolimbata_, in Celebes, 463
Palaearctic Region, limits of, 39
characteristic features of, 41
Palaeozoic formations, depth of, round London, 218
Palm confined to Round Island, 444
Panax, fossil in Greenland, 186
Papilio, 17
Paraguay, no wild horses or cattle in, 226
Parnassius, Palaearctic, 42
_Parus ater_, 19
_P. borealis_, 19, 64
_P. britannicus_, 321
_P. camtschatkensis_, 19
_P. cinctus_, 20
_P. coeruleus_, 20
_P. cyaneus_, 20
_P. cristatus_, 20
_P. ledouci_, 20
_P. lugubris_, 20
_P. major_, 19
_P. palustris_, 19; discontinuous area of, 65
_P. rosea_, 340
_P. teneriffae_, 20
Passeres of the Sandwich Islands, 314
Past changes of New Zealand, 478
Payer, Lieut., on evaporation of ice during the Arctic summer, 140
Peculiar fauna of New Zealand, deductions from, 484
Pengelly, Mr., on submerged forests, 335
_Pennula millei_, in Sandwich Islands, 313
Permanence of continents, summary of evidence for, 103
Permian formation, indications of ice-action in, 200
Perodicticus, a local genus, 26
_Petroselinum segetum_, on railway bank, 514
{560}
Philippine Islands, 387
mammalia of, 387
birds of, 388
past history of, 389
_Phyllodactylus galapagensis_, 279
_Phylloscopus borealis_, range of, 15
Physical causes which determine distribution, 533
features of Formosa, 401
Pica, 17
Pickering, Dr., on the flora of the Sandwich Islands, 323
on temperate forms on mountains of the Sandwich Islands, 323
_Pithecia monachus_, distribution of, 18
_P. rufibarbata_, 18
Pitta, distribution of, 25
Plants, dispersal of, 80
seeds of, adapted for dispersal, 80
wide range of species and genera of, 185
poverty of, in Ireland, 339
peculiar British, 359
of Ireland not in Great Britain, 364
cause of their wide diffusion and narrow restriction, 369
easily dispersed often have restricted ranges, 504
how they migrate from north to south, 512
of existing genera throughout the Tertiary period, 520
southern migration of, by way of the Himalayas, 523
southern migration of, through Africa, 524
endemic genera of, in New Zealand, 526
Platypus, 30
_Plestiodon longirostris_ of Bermuda, 266
Po, matter carried away by, 173
Podargus, Australian genus, 47
Poecilozonites, peculiar to Bermuda, 270
_Poinciana regia_ in Madagascar, 440
Populus, fossil in Spitzbergen, 184
Pourtales, Count, on modern formation of chalk, 95
on sedimentary deposits in Gulf of Mexico, 222
Poverty in species of Britain, 338
Precession of Equinoxes, influence of, on climate, 126
Preservation of species, 63
Proboscidea, range of, 30
Proteus, why preserved, 63
Psophia, range of species of, 18
Pteroptochidae, 29
Pyrenean ibex, restricted range of, 15

R.
Railways, new plants on, 513
Ramsay, Mr. Wardlaw, on Philippine birds, 388
Professor, on ancient land surfaces, 99
on geological time 212
on thickness of sedimentary rocks, 219
Rat, native, of New Zealand, 475
Rate of organic change usually measured by an incorrect scale, 232
Rats in the Galapagos, 278
Raven, wide range of, 15
Reade, T. Mellard, on changes of sea and land, 84
Recent continental islands, 243, 331
Red clay of Bermuda, 265
Reptiles, dispersal of, 75
of the Galapagos, 278
of the Sandwich Islands, 316
cause of scarcity of, in British Isles, 339
of Madagascar, 417
of the Seychelles, 430
of Mauritius and Round Island, 438
of New Zealand, 483
_Rhodolaena altivola_ in Madagascar, 440
_Rhus toxicodendron_ in Bermuda, 272
Ridgway, Mr., on birds of Galapagos, 281
River-channels, buried, 336
_Roches moutonnees_, 108
Rodents in Madagascar, 417
Round Island, a snake and a palm peculiar to, 438, 444
_Rumex pulcher_ in New Zealand, 515
Rye, Mr. E. C., on peculiar British insects, 345, 351

S.
St. Helena, 292
effects of European occupation on the vegetation of, 294
insects of, 298
land-shells of, 304
absence of fresh-water organisms in, 304
native vegetation of, 305
Salvin, Mr., on the birds of the Galapagos, 280
Sandwich Islands, the, 310
zoology of, 313
birds of, 313
reptiles of, 316
land-shells of, 316
insects of, 318
vegetation of, 321
antiquity of fauna and flora of, 328
Sassafras, in Swiss Miocene, 183
Scandinavian flora, aggressive power of, 511
Scientific voyages, comparative results of, 7
Sciurus, 26
Sclater, Mr. P. L., on zoological region, 32, 39
Scotland, glacial deposits of, 112-115
probable rate of denudation in, 173
Miocene flora of, 184
peculiar fishes of, 341
{561}
_Scotophilus tuberculatus_ in New Zealand, 474
Scrophularincae, why few species are common to Australia and New Zealand,
505
Sea, depth of, around Madagascar, 414
depth of, around Celebes, 452
Sea-bottom around New Zealand and Australia, 473
Sea-level, changes of, dependent on glaciation, 161
complex effects of glaciation on, 162, 164
rise of, a cause of denudation, 174
Seas, inland, in Tertiary period, 191
Section of sea-bottom near Bermuda, 264
Sedges and grasses common to Australia and New Zealand, 504
Sedimentary rocks, how to estimate thickness of, 217
thinning out of, 217
how formed, 218
thickness of, 217, 221
summary of conclusions on the rate of formation of the, 221
Seebohm, Mr., on _Parus palustris_, 65
on _Emberiza schoeniclus_, 66
on snow in Siberia, 166
on birds of Japan, 396
Seeds, dispersal of, 257
carried by birds, 258
_Senecio australis_, on burnt ground, 513
Sericinus, Palaearctic, 42
Seychelles Archipelago, 429
birds of, 430
reptiles and amphibia of, 430
fresh-water fishes of, 433
land-shells of, 434
Sharp, Dr. D., on beetles of the Sandwich Islands, 319
on peculiar British beetles, 345
Shells, peculiar to Britain, 356
Shetland Isles, peculiar beetle of, 354
Shore deposits, 85, 211
proving the permanence of continents, 97
distance from coast of, 221
_Sialia sialis_, variation of, 58
Siberia, amount of snow and its sudden disappearance in, 166
Silurian boulder-beds, 201
warm Arctic climate, 202
Simiidae, 27
_Sisyrinchium bermudianum_, 272
Skertchley, Mr., on four distinct boulder-clays, 118
on Tertiary deposits in Egypt and Nubia, 191
on climatic stability of present epoch, 233
Slug peculiar to Ireland, 356
Snake peculiar to Round Island, 438
Snakes of the Galapagos, 280
of the Seychelles, 431
Snow and ice, properties of, in relation to climate, 131
Snow, effects of, on climate, 133
Snow, quantity of heat required to melt, 134
often of small amount in high latitudes, 135
never perpetual on lowlands, 136
conditions determining perpetual, 137
maintains cold by reflecting the solar heat, 144
Snow-line, alterations of, causing migration of plants, 516
Sollas, Mr. J. W., on greater intensity of telluric action in past time,
223
South Africa, recent glaciation of, 163
many northern genera of plants in, 524
its supposed connection with Australia, 525
South American plants in New Zealand, 521
South Temperate America, poor in species, 53
climate of, 146
Southern flora, comparative tenderness of, 528
Southern plants, why absent in the Northern Hemisphere, 527
Space, temperature of, 129
Specialisation antagonistic to diffusion of _species_, 505
Species, origin of new, 56
extinction of, 63
rise and decay of, 64
epoch of exceptional stability of, 232
dying out and replacement of, 409
preservation of, in islands, 410
Specific areas, 14; discontinuous, 64
_Spiranthes romanzoviana_, 364
Spitzbergen, Miocene flora of, 184
absence of boulder-beds in, 187
Spruce, Dr. Richard, on the dispersion of hepaticae, 309
Stability of extreme glacial conditions, 159
Stainton, Mr. H. T., on peculiar British moths, 346-350
Stanivoi mountains, why not ice-clad, 154
Starlings, genera of, in New Zealand, 482
_Stellaria media_, temporary appearance of, 515
Sternum, process of abortion of keel of, 437
Stow, Mr. G. W., on glacial phenomena in South Africa, 163
Stratified rocks formed near shores, 85, 87
deposits, how formed, 218
Striated rocks, 107
blocks in the Permian formation, 200
_Striae flammea_, range of, 15
Struthiones, 30
Struthious birds of New Zealand as indicating past changes, 478
Stylidium, wide range of, 185
Submerged forests, 334
{562}
Subsidence of isthmus of Panama, 151
Sumatra, geology of, 385
Sweden, two deposits of "till" in, 121
Swimming powers of mammalia, 74
Swinhoe, Mr. Robert, researches in Formosa, 400
Switzerland, interglacial warm periods in, 121
Sylviadae, overlapping genera of, 29

T.
Talpidae, a Palaearctic group, 41
Tapirs, distribution of, 25
former wide range of, 393
Tarsius, 63
_Tarsius spectrum_ in Celebes, 456
Tasmania and North Australia, resemblance of, 5
route of Arctic plants to, 520
_Taxodium distichum_ in Spitzbergen, 184
Temperate climates in Arctic regions, 181
Australian genera of plants in New Zealand, 502
Australian species of plants in New Zealand, 502
Temperature, how dependent on sun's distance, 129
of space, 129
Tertiary glacial epochs, evidence against, 179
warm climates, continuous, 187
Test of glaciation at any period, 175
_Testudo abingdonii_, 279
_T. microphyes_, 278
Tetraogallus, distribution of, 24
Thais, a Palaearctic genus, 42
Thomson, Sir William, on age of the earth, 213
Sir Wyville, on organisms in the globigerina-ooze, 89
analysis of globigerina-ooze, 91
_Thryothorus bewickii_, discontinuity of, 68
"Till" of Scotland, 112
several distinct formations of, 121
Tits, distribution of species of, 19
Torreya, fossil in Spitzbergen, 186
Tortoises of the Galapagos, 278
Trade-winds, how modified by a glacial epoch, 142
Tragulidae, 27
Travelled blocks, 109
Tremarctos, an isolated genus, 29
Triassic warm Arctic climate, 200
Tribonyx not a New Zealand genus, 483
Trichoptera peculiar to Britain, 355
Trogons, distribution of, 28
Tropical affinities of New Zealand birds, 483
character of the New Zealand flora, cause of, 500
genera common to New Zealand and Australia, 501
Turdus, 17, 26
_Turdus fuscescens_, variation of, 58, 59
Tylor, A., on estimating the rate of denudation, 214
Tyrannidae, an American family, 50

U.
Uraniidae, 28
Uropeltidae, 30
Urotrichus, distribution of, 25
Ursus, 26

V.
Variation in animals, 57
amount of, in N. American birds, 58
Vegetation, local peculiarities of, 185
effects of Polar night on, 198
_Vesperugo serotinus_, range of, 14
_Vireo bellii_, supposed discontinuity of, 68
Vireonidae, an American family, 49

W.
Wallich, Dr., on habitat of globigerinae, 92
Warren, Mr. W., information on British lepidoptera, 347
Water, properties of, in relation to climate, 131, 133
Waterhouse, Mr., on Galapagos beetles, 284
Wales, peculiar fish of, 341
Warm climates of northern latitudes, long persistence of, 201
Watson, Mr. H. C., on the flora of the Azores, 256
on peculiar British plants, 359
on vegetation of railway banks, 513
Webb, Mr., on comparison of Mars and the Earth, 166
West Australia, rich flora of, 494
former extent and isolation of, 497
West Indies, a Neotropical district, 53
White, Dr. F. Buchanan, on the Hemiptera of St. Helena, 303
Mr. John, on native accounts of the moa, 477
Whitehead, Mr. John, on Bornean birds, 377
Wilson, Mr. Scott B., on birds of the Sandwich Islands, 314
Winged birds of New Zealand, 482
Wingless birds never inhabit continents, 437
their evidence against "Lemuria," 438
of New Zealand, 476
Wings of struthious birds show retrograde development, 437
{563}
Winter temperature of Europe and America, 196
Wolf, range of, 14
Wollaston, Mr. T. V., on insular character of St. Helena, 294
on St. Helena shells and insects, 297
Wood, Mr. Searles V., jun., on formation of "till," 114
on alternations of climate, 118
on causes of glacial epochs, 125
conclusive objection to the excentricity theory, 160
on continuous warm Tertiary climates, 180
Woodward, Dr. S. P., on Ammonites living in shallow water, 95
Woodward, Mr., on "Lemuria," 426
Wright, Dr. Percival, on lizards of the Seychelles, 431

Y.
Young, Professor J., on contemporaneous formation of deposits, 221
Young Island, lofty Antarctic, 522

Z.
Zoology of the Azores, 248
of Bermuda, 262
of the Sandwich Islands, 313
of Borneo, 376
of Madagascar, 416
of islands round Celebes, 453
of Celebes, 455
Zoological and geographical regions compared, 32, 54
Zoological features of Japan, 393
character of New Zealand, 473

THE END

{564}

RICHARD CLAY AND SONS, LIMITED, LONDON AND BUNGAY.

* * * * *

[1] A small number of species belonging to the West Indies are found in the extreme southern portion of the Florida Peninsula.

[2] I cannot avoid here referring to the enormous waste of labour and money with comparatively scanty and unimportant results to natural history of most of the great scientific voyages of the various civilized governments during the present century. All these expeditions combined have done far less than private collectors in making known the products of remote lands and islands. They have brought home fragmentary collections, made in widely scattered localities, and these have been usually described in huge folios or quartos, whose value is often in inverse proportion to their bulk and cost. The same species have been collected again and again, often described several times over under new names, and not unfrequently stated to be from places they never inhabited. The result of this wretched system is that the productions of some of the most frequently visited and most interesting islands on the globe are still very imperfectly known, while their native plants and animals are being yearly exterminated, and this is the case even with countries under the rule or protection of European governments. Such are the Sandwich Islands, Tahiti, the Marquesas, the Philippine Islands, and a host of smaller ones; while Bourbon and Mauritius, St. Helena, and several others, have only been adequately explored after an important portion of their productions has been destroyed by cultivation or the reckless introduction of goats and pigs. The employment in each of our possessions, and those of other European powers, of a resident naturalist at a very small annual expense, would have done more for the advancement of knowledge in this direction than all the expensive expeditions that have again and again circumnavigated the globe.

[3] The general facts of Palaeontology, as bearing on the migrations of animal groups, are summarised in my _Geographical Distribution of Animals_, Vol. I. Chapters VI., VII., and VIII.

[4] Since these lines were written, a fine series of specimens of this rare humming-bird has been obtained from the same locality. (See _Proc. Zool. Soc._ 1881, pp. 827-834.)

[5] Many of these large genera are now subdivided, the divisions being sometimes termed genera, sometimes sub-genera.

[6] The Palaearctic region includes temperate Asia and Europe, as will be explained in the next chapter.

[7] The following list of the genera of reptiles and amphibia peculiar to the Palaearctic Region has been furnished me by Mr. G. A. Boulenger, of the British Museum:--

SNAKES. FROGS AND TOADS.

_Achalinus_--China, Japan. _Pelobates_--Eur., S.W. Asia.
_Coelopeltis_--S. Eur., N. Af., _Pelodytes_--W. Europe.
S.W. Asia. _Discoglossus_--S. Eur., N.W. Af.
_Macroprotodon_--S. Eur., N. Af. _Bombinator_--Eur., Temp. Asia.
_Taphrometopon_--Cent. Asia. _Alytus_--Cent. and W. Eur.

LIZARDS. NEWTS.

_Phrynocephalus_--Cent. and S.W. _Salamandra_--Eur., N. Af., S.W.
Asia. Asia.
_Anguis_--Europe, W. Asia. _Chioglossa_--Spain and Portugal.
_Blanus_--S.W. Eur., N.W. Africa, _Salamandrina_--Italy.
S.W. Asia. _Pachytriton_--East Thibet.
_Trogonophis_--N.W. Africa. _Hynobius_--China and Japan.
_Lacerta_--Eur., Temp. Asia, N. _Geomolge_--E. Manchuria.
Africa (one sp. in _Onychodactylus_--Japan.
W. Af.). _Salamandrella_--Siberia.
_Psammodromus_--S.W. Eur., N.W. _Ranidens_--Siberia.
Africa. _Batrachyperus_--East Thibet.
_Algiroides_--S. Eur. _Myalobatrachus_--China, Japan.
_Proteus_--Caverns of S. Austria.

[8] Remains of the dingo have been found fossil in Pleistocene deposits but the antiquity of man in Australia is not known. It is not, however, improbable that it may be as great as in Europe. My friend A. C. Swinton, Esq., while working in the then almost unknown gold-field of Maryborough, Victoria, in January, 1855, found a fragment of a well-formed stone axe resting on the metamorphic schistose bed-rock about five feet beneath the surface. It was overlain by the compact gravel drift called by the miners "cement," and by an included layer of hard iron-stained sandstone. The fragment is about an inch and three-eighths wide and the same length, and is of very hard fine-grained black basalt. One side is ground to a very smooth and regular surface, terminating in a well-formed cutting edge more than an inch long, the return face of the cutting part being about a quarter of an inch wide. The other side is a broken surface. The weapon appears to have been an axe or tomahawk closely resembling that figured at p. 335 of Lumholtz's _Among Cannibals_, from Central Queensland. The fragment was discovered by Mr. Swinton and the late Mr. Mackworth Shore, one of the discoverers of the gold-field, before any rush to it had taken place, and it seems impossible to avoid the conclusion that it was formed prior to the deposit of the gravel drift and iron-stained sandstone under which it lay. This would indicate a great antiquity of man in Australia, and would enable us to account for the fossilised remains of the dingo in Pleistocene deposits as those of an animal introduced by man.

[9] These facts are taken from a memoir on _The Mammals and Winter Birds of Florida_, by J. A. Allen; forming Vol. II., No. 3, of the Bulletin of the Museum of Comparative Zoology at Harvard College, Cambridge, Massachusetts.

[10] The great variation in wild animals is more fully discussed and illustrated in the author's _Darwinism_ (Chapter III.).

[11] See _Ibis_, 1879, p. 32.

[12] In Mr. Seebohm's latest work, _Birds of the Japanese Empire_ (1890), he says, "Examples from North China are indistinguishable from those obtained in Greece" (p. 82).

[13] _Ibis_, 1879, p. 40. In his _Birds of the Japanese Empire_ (1890), Mr. Seebohm classes the Japanese and European forms as _E. schoeniclus_, and thinks that their range is probably continuous across the two continents.

[14] Lyell's _Principles of Geology_, ii., p. 369.

[15] Mr. Darwin found that the large _Helix pomatia_ lived after immersion in sea-water for twenty days. It is hardly likely that this is the extreme limit of their powers of endurance, but even this would allow of their being floated many hundred miles at a stretch, and if we suppose the shell to be partially protected in the crevice of a log of wood, and to be thus out of water in calm weather, the distance might extend to a thousand miles or more. The eggs of fresh-water mollusca, as well as the young animals, are known to attach themselves to the feet of aquatic birds, and this is probably the most efficient cause of their very wide diffusion.

[16] _Principles of Geology_, 11th Ed., Vol. I., p. 258.

[17] On Limestone as an Index of Geological Time.

[18] In his _Preliminary Report on Oceanic Deposit_, Mr. Murray says:--"It has been found that the deposits taking place near continents and islands have received their chief characteristics from the presence of the _debris_ of adjacent lands. In some cases these deposits extend to a distance of over 150 miles from the coast." (_Proceedings of the Royal Society_, Vol. XXIV. p. 519.)

"The materials in suspension appear to be almost entirely deposited within 200 miles of the land." (_Proceedings of the Royal Society of Edinburgh_, 1876-77, p. 253.)

[19] _Geographical Evolution. (Proceedings of the Royal Geographical Society._ 1879, p. 426.)

[20] Professor Dana was, I believe, the first to point out that the regions which, after long undergoing subsidence and accumulating vast piles of sedimentary deposit have been elevated into mountain ranges, thereby become stiff and unyielding, and that the next depression and subsequent upheaval will be situated on one or the other sides of it; and he has shown that, in North America, this is the case with all the mountains of the successive geological formations. Thus, depressions, and elevations of extreme slowness but often of vast amount, have occurred successively in restricted adjacent areas; and the effect has been to bring each portion in succession beneath the ocean but always bordered on one or both sides by the remainder of the continent, from the denudation of which the deposits are formed which, on the subsequent upheaval, become mountain ranges. (_Manual of Geology_, 2nd Ed., p. 751.)

[21] _Nature_, Vol. II., p. 297.

[22] Sir W. Thomson, _Voyage of Challenger_, Vol. II., p. 374.

[23] The following is the analysis of the chalk at Oahu:--

Carbonate of Lime 92.800 per cent.
Carbonate of Magnesia 2.385 ,,
Alumina 0.250 ,,
Oxide of Iron 0.543 ,,
Silica 0.750 ,,
Phosphoric Acid and Fluorine 2.113 ,,
Water and loss 1.148 ,,

This chalk consists simply of comminuted corals and shells of the reef. It has been examined microscopically and found to be destitute of the minute organisms abounding in the chalk of England. (_Geology of the United States Exploring Expedition_, p. 150.) Mr. Guppy also found chalk-like coral limestones containing 95 p.c. of carbonate of lime in the Solomon Islands.

The absence of _Globigerinae_ is a local phenomenon. They are quite absent in the Arafura Sea, and no _Globigerina_-ooze was found in any of the enclosed seas of the Pacific, but with these exceptions the _Globigerinae_ "are really found all over the bottom of the ocean." (Murray on Oceanic Deposits--_Proceedings of Royal Society_, Vol. XXIV., p. 523.)

The above analysis shows a far closer resemblance to chalk than that of the _Globigerina_-ooze of the Atlantic, four specimens of which given by Sir W. Thomson (_Voyage of the Challenger_ Vol. II. Appendix, pp. 374-376, Nos. 9, 10, 11 and 12) from the mid-Atlantic, show the following proportions:--

Carbonate of Lime 43.93 to 79.17 per cent.
Carbonate of Magnesia 1.40 to 2.58 ,,
Alumina and Oxide of Iron 6.00? to 32.98 ,,
Silica 4.60 to 11.23 ,,

In addition to the above there is a quantity of insoluble residue consisting of small particles of sanidine, augite, hornblende, and magnetite, supposed to be the product of volcanic dust or ashes carried either in the air or by ocean currents. This volcanic matter amounts to from 4.60 to 8.33 per cent. of the _Globigerina_-ooze of the mid-Atlantic, where it seems to be always present; and the small proportion of similar matter in true chalk is another proof that its origin is different, and that it was deposited far more rapidly than the oceanic ooze.

The following analysis of chalk by Mr. D. Forbes will show the difference between the two formations:--

Grey Chalk, White Chalk,
_Folkestone_. _Shoreham_.

Carbonate of Lime 94.09 98.40
Carbonate of Magnesia 0.31 0.08
Alumina and Phosphoric Acid a trace 0.42
Chloride of Sodium 1.29 --
Insoluble debris 3.61 1.10

(From _Quarterly Journal of the Geological Society_, Vol. XXVII.)

The large proportion of carbonate of lime, and the very small quantity of silica, alumina, and insoluble _debris_, at once distinguish true chalk from the _Globigerina_-ooze of the deep ocean bed.

[24] Notes on Reticularian Rhizopoda; in _Microscopical Journal_, Vol. XIX., New Series, p. 84.

[25] _Proceedings of the Royal Society_, Vol. XXIV. p. 532.

[26] See Presidential Address in Sect. D. of British Association at Plymouth, 1877.

[27] _Geological Magazine_, 1871, p. 426.

[28] In his lecture on _Geographical Evolution_ (which was published after the greater part of this chapter had been written) Sir Archibald Geikie expresses views in complete accordance with those here advocated. He says:--"The next long era, the Cretaceous, was more remarkable for slow accumulation of rock under the sea than for the formation of new land. During that time the Atlantic sent its waters across the whole of Europe and into Asia. But they were probably nowhere more than a few hundred feet deep over the site of our continent, even at their deepest part. Upon their bottom there gathered a vast mass of calcareous mud, composed in great part of foraminifera, corals, echinoderms, and molluscs. Our English chalk, which ranges across the north of France, Belgium, Denmark, and the north of Germany, represents a portion of the deposits of that sea-floor." The weighty authority of the Director-General of the Geological Survey may perhaps cause some geologists to modify their views as to the deep-sea origin of chalk, who would have treated any arguments advanced by myself as not worthy of consideration.

[29] _Introduction and Succession of Vertebrate Life in America_, by Professor O. C. Marsh. Reprinted from the _Popular Science Monthly_, March, April, 1878.

[30] _Physical Geography and Geology of Great Britain_, 5th Ed. p. 61.

[31] Of late it has been the custom to quote the so-called "ridge" down the centre of the Atlantic as indicating an extensive ancient land. Even Professor Judd at one time adopted this view, speaking of the great belt of Tertiary volcanoes "which extended through Greenland, Iceland, the Faroe Islands, the Hebrides, Ireland, Central France, the Iberian Peninsula, the Azores, Madeira, Canaries, Cape de Verde Islands, Ascension, St. Helena, and Tristan d'Acunha, and which constituted as shown by the recent soundings of H.M.S. _Challenger_ a mountain-range, comparable in its extent, elevation, and volcanic character with the Andes of South America" (_Geological Mag._ 1874, p. 71). On examining the diagram of the Atlantic Ocean in the _Challenger Reports_, No. 7, a considerable part of this ridge is found to be more than 1,900 fathoms deep, while the portion called the "Connecting Ridge" seems to be due in part to the deposits carried out by the River Amazon. In the neighbourhood of the Azores, St. Paul's Rocks, Ascension, and Tristan d'Acunha are considerable areas varying from 1,200 to 1,500 fathoms deep, while the rest of the ridge is usually 1,800 or 1,900 fathoms. The shallower water is no doubt due to volcanic upheaval and the accumulation of volcanic ejections, and there may be many other deeply submerged old volcanoes on the ridge; but that it ever formed a chain of mountains "comparable in elevation with the Andes," there seems not a particle of evidence to prove. It is however probable that this ridge indicates the former existence of some considerable Atlantic islands, which may serve to explain the presence of a few identical genera, and even species of plants and insects in Africa and South America, while the main body of the fauna and flora of these two continents remains radically distinct.

In my _Darwinism_ (pp. 344-5) I have given an additional argument founded on the comparative height and area of land with the depth and area of ocean, which seems to me to add considerably to the weight of the evidence here submitted for the permanence of oceanic and continental areas.

[32] In a review of Mr. T. Mellard Reade's _Chemical Denudation and Geological Time_, in _Nature_ (Oct. 2nd, 1879), the writer remarks as follows:--"One of the funny notions of some scientific thinkers meets with no favour from Mr. Reade, whose geological knowledge is practical as well as theoretical. They consider that because the older rocks contain nothing like the present red clays, &c., of the ocean floor, that the oceans have always been in their present positions. Mr. Reade points out that the first proposition is not yet proved, and the distribution of animals and plants and the fact that the bulk of the strata on land are of marine origin are opposed to the hypothesis." We must leave it to our readers to decide whether the "notion" developed in this chapter is "funny," or whether such hasty and superficial arguments as those here quoted from a "practical geologist" have any value as against the different classes of facts, all pointing to an opposite conclusion, which have now been briefly laid before them, supported as they are by the expressed opinion of so weighty an authority as Sir Archibald Geikie, who, in the lecture already quoted says:--"From all this evidence we may legitimately conclude that the present land of the globe, though formed in great measure of marine formations, has never lain under the deep sea; but that its site must always have been near land. Even its thick marine limestones are the deposits of comparatively shallow water."

[33] _Antiquity of Man_, 4th Ed. pp. 340-348.

[34] _The Great Ice Age and its Relation to the Antiquity of Man._ By James Geikie, F.R.S. (Isbister and Co., 1874.)

[35] This view of the formation of "till" is that adopted, by Dr. Geikie, and upheld by almost all the Scotch, Swiss, and Scandinavian geologists. The objection however is made by many eminent English geologists, including the late Mr. Searles V. Wood, Jun., that mud ground off the rocks cannot remain beneath the ice, forming sheets of great thickness, because the glacier cannot at the same time grind down solid rock and yet pass over the surface of soft mud and loose stones. But this difficulty will disappear if we consider the numerous fluctuations in the glacier with increasing size, and the additions it must have been constantly receiving as the ice from one valley after another joined together, and at last produced an ice-sheet covering the whole country. The grinding power is the motion and pressure of the ice, and the pressure will depend on its thickness. Now the points of maximum thickness must have often changed their positions, and the result would be that the matter ground out in one place would be forced into another place where the pressure was less. If there were no lateral escape for the mud, it would necessarily support the ice over it just as a water-bed supports the person lying on it; and when there was little drainage water, and the ice extended, say, twenty miles in every direction from a given part of a valley where the ice was of less than the average thickness, the mud would necessarily accumulate at this part simply because there was no escape for it. Whenever the pressure all round any area was greater than the pressure on that area, the _debris_ of the surrounding parts would be forced into it, and would even raise up the ice to give it room. This is a necessary result of hydrostatic pressure. During this process the superfluous water would no doubt escape through fissures or pores of the ice, and would leave the mud and stones in that excessively compressed and tenacious condition in which the "till" is found. The unequal thickness and pressure of the ice above referred to would be a necessary consequence of the inequalities in the valleys, now narrowing into gorges, now opening out into wide plains, and again narrowed lower down; and it is just in these openings in the valleys that the "till" is said to be found, and also in the lowlands where an ice-sheet must have extended for many miles in every direction. In these lowland valleys the "till" is both thickest and most wide-spread, and this is what we might expect. At first, when the glaciers from the mountains pushed out into these valleys, they would grind out the surface beneath them into hollows, and the drainage-water would carry away the _debris_. But when they spread all over the surface from sea to sea, and there was little or no drainage water compared to the enormous area covered with ice, the great bulk of the _debris_ must have gathered under the ice wherever the pressure was least, and the ice would necessarily rise as it accumulated. Some of the mud would no doubt be forced out along lines of least resistance to the sea, but the friction of the stone-charged "till" would be so enormous that it would be impossible for any large part of it to be disposed of in this way.

[36] That the ice-sheet was continuous from Scotland to Ireland is proved by the glacial phenomena in the Isle of Man, where "till" similar to that in Scotland abounds, and rocks are found in it which must have come from Cumberland and Scotland, as well as from the north of Ireland. This would show that glaciers from each of these districts reached the Isle of Man, where they met and flowed southwards down the Irish Sea. Ice-marks are traced over the tops of the mountains which are nearly 2,000 feet high. (See _A Sketch of the Geology of the Isle of Man_, by John Horne, F.G.S. _Trans. of the Edin. Geol. Soc._ Vol. II. pt. 3, 1874.)

[37] _The Great Ice Age_, p. 177.

[38] These are named, in descending order, Hessle Boulder Clay, Purple Boulder Clay, Chalky Boulder Clay, and Lower Boulder Clay--below which is the Norwich Crag.

[39] "On the Climate of the Post-Glacial Period." _Geological Magazine_, 1872, pp. 158, 160.

[40] _Geological Magazine_, 1876, p. 396.

[41] _Early Man in Britain and his Place in the Tertiary Period_, p. 113.

[42] Heer's _Primaeval World of Switzerland_ Vol. II., pp. 148-168.

[43] Dr. James Geikie in _Geological Magazine_, 1878, p. 77.

[44] This subject is admirably discussed in Professor Asa Gray's Lecture on "Forest Geography and Archaeology" in the _American Journal of Science and Arts_, Vol. XVI. 1878.

[45] In a letter to _Nature_ of October 30th, 1879, the Rev. O. Fisher calls attention to a result arrived at by Pouillet, that the temperature which the surface of the ground would assume if the sun were extinguished would be -128deg F. instead of -239deg F. If this corrected amount were used in our calculations, the January temperature of England during the glacial epoch would come out 17deg F., and this Mr. Fisher thinks not low enough to cause any extreme difference from the present climate. In this opinion, however, I cannot agree with him. On the contrary, it would, I think, be a relief to the theory were the amounts of decrease of temperature in winter and increase in summer rendered more moderate, since according to the usual calculation (which I have adopted) the differences are unnecessarily great. I cannot therefore think that this modification of the temperatures, should it be ultimately proved to be correct (which is altogether denied by Dr. Croll), would be any serious objection to the adoption of Dr. Croll's theory of the Astronomical and Physical causes of the Glacial Epoch.

The reason of the theoretical increase of summer heat being greater than the decrease of winter cold is because we are now nearest the sun in winter and farthest in summer, whereas we calculate the temperatures of the glacial epoch for the phase of precession when the _aphelion_ was in winter. A large part of the increase of temperature would no doubt be used up in melting ice and evaporating water, so that there would be a much less increase of sensible heat; while only a portion of the theoretical lowering of temperature in winter would be actually produced owing to equalising effect of winds and currents, and the storing up of heat by the earth and ocean.

[46] Dr. Croll says this "is one of the most widespread and fundamental errors within the whole range of geological climatology." The temperature of the snow itself is, he says, one of the main factors. (_Climate and Cosmology_, p. 85.) But surely the temperature of the snow must depend on the temperature of the air through which it falls.

[47] In an account of Prof. Nordenskjoeld's recent expedition round the northern coast of Asia, given in _Nature_, November 20th, 1879, we have the following passage, fully supporting the statement in the text. "Along the whole coast, from the White Sea to Behring's Straits, no glacier was seen. During autumn the Siberian coast is nearly free of ice and snow. There are no mountains covered all the year round with snow, although some of them rise to a height of more than 2,000 feet." It must be remembered that the north coast of Eastern Siberia is in the area of supposed greatest winter cold on the globe.

[48] Dr. Croll objects to this argument on the ground that Greenland and the Antarctic continent are probably lowlands or groups of islands. (_Climate and Cosmology_, Chap. V.)

[49] "On the Glacial Epoch," by James Croll. _Geol. Mag._ July, August, 1874.

[50] "The general absence of recent marks of glacial action in Eastern Europe is well known; and the series of changes which have been so well traced and described by Prof. Szabo as occurring in those districts seems to leave no room for those periodical extensions of 'ice-caps' with which some authors in this country have amused themselves and their readers. Mr. Campbell, whose ability to recognise the physical evidence of glaciers will scarcely be questioned, finds quite the same absence of the proof of extensive ice-action in North America, westward of the meridian of Chicago." (Prof. J. W. Judd in _Geol. Mag._ 1876, p. 535.)

The same author notes the diminution of marks of ice-action on going eastward in the Alps; and the Altai Mountains far in Central Asia show no signs of having been largely glaciated. West of the Rocky Mountains, however, in the Sierra Nevada and the coast ranges further north, signs of extensive old glaciers again appear; all which phenomena are strikingly in accordance with the theory here advocated, of the absolute dependence of glaciation on abundant rainfall and elevated snow-condensers and accumulators.

[51] I have somewhat modified this whole passage in the endeavour to represent more accurately the difference between the views of Dr. Croll and Sir Charles Lyell.

[52] For numerous details and illustrations see the paper--"On Ocean Currents in Relation to the Physical Theory of Secular Changes of Climate"--in the _Philosophical Magazine_, 1870.

[53] See _Darwin's Naturalist's Voyage Round the World_, 2nd Edition, pp. 244-251.

[54] The influence of geographical changes on climate is now held by many geologists who oppose what they consider the extravagant hypotheses of Dr. Croll. Thus, Prof. Dana imputes the glacial epoch chiefly, if not wholly, to elevation of the land caused by the lateral pressure due to shrinking of the earth's crust that has caused all other elevations and depressions. He says: "Now, that elevation of the land over the higher latitudes which brought on the glacial era is a natural result of the same agency, and a natural, and almost necessary, counterpart of the coral-island subsidence which must have been then in progress. The accumulating, folding, solidification, and crystallisation of rocks attending all the rock-making and mountain-making through the Palaeozoic, Mesozoic, and Cenozoic eras, had greatly stiffened the crust in these parts; and hence in after times, the continental movements resulting from the lateral pressure necessarily appeared over the more northern portions of the continent, where the accumulations and other changes had been relatively small. To the subsidence which followed the elevation the weight of the ice-cap may have contributed in some small degree. But the great balancing movements of the crust of the continental and oceanic areas then going forward must have had a greatly preponderating effect in the oscillating agency of all time--lateral pressure within the crust." (_American Journal of Science and Arts_, 3rd Series, Vol. IX. p. 318.)

"In the 2nd edition of his _Manual of Geology_, Professor Dana suggests elevation of Arctic lands sufficient to exclude the Gulf Stream, as a source of cold during glacial epochs. This, he thinks, would have made an epoch of cold at any era of the globe. A deep submergence of Behring's Strait, letting in the Pacific warm current to the polar area, would have produced a mild Arctic climate like that of the Miocene period. When the warm current was shut out from the polar area it would yet reach near to it, and bring with it that abundant moisture necessary for glaciation." (_Manual of Geology_, 2nd Edition, pp. 541-755, 756.)

[55] Dana's _Manual of Geology_, 2nd Edition, p. 540.

[56] Dr. Croll says that I here assume an impossible state of things. He maintains "that the change from the distant sun in winter, and near sun in summer to the near sun in winter and distant sun in summer, aided by the change in the physical causes which this would necessarily bring about, would certainly be sufficient to cause the snow and ice to disappear." (_Climate and Cosmology_, p. 106.) But I demur to his "necessarily." It is not the _direct_ effect of the nearer sun in winter that is supposed to melt the snow and ice, but the "physical causes," such as absence of fogs and increase of warm equatorial currents. But the near sun in winter acting on an ice-clad surface would only increase the fogs and snow, while the currents could only change if a large portion of the ice were first melted, in which case they would no doubt be modified so as to cause a further melting of the ice. Dr. Croll says: "The warm and equable conditions of climate which would then prevail, and the enormous quantity of intertropical water carried into the Southern Ocean, would soon produce a melting of the ice." (_Loc. cit._ p. 111.) This seems to me to be assuming the very point at issue. He has himself shown that the presence of large quantities of ice prevents "a warm and equable climate" however great may be the sun-heat; the ice therefore would _not_ be melted, and there would be no increased flow of intertropical water to the Southern Ocean. The ocean currents are mainly due to the difference of temperature of the polar and equatorial areas combined with the peculiar form and position of the continents, and some one or more of these factors must be altered _before_ the ocean currents towards the north pole can be increased. The only factor available is the Antarctic ice, and if this were largely increased, the northward-flowing currents might be so increased as to melt some of the Arctic ice. But the very same argument applies to both poles. Without some geographical change the Antarctic ice could not materially diminish during its winter in _perihelion_, nor increase to any important extent during the opposite phase. We therefore seem to have no available agency by which to get rid of the ice over a glaciated hemisphere, _so long as the geographical conditions remained unchanged and the excentricity continued high_.