Chapter VI: The Work of the Ocean (3)

Another substance which is somewhat widespread in the ocean-bottom is _phosphate of lime_, which occurs in various sorts of oozes, in the manganiferous nodules, in glauconite, and in independent nodules. Like the grains of glauconite, the grains of phosphate of lime appear to have started as concretions in shells, and to be the result of the reaction of organic matter on the contents of sea-water. The immediate source of the lime phosphate in the water appears to have been the shells or bones of the numerous animals living in the sea.

Secondary minerals made from the constituents of volcanic matter which has been decomposed occur not uncommonly in the bottom of the sea. These minerals belong to the general class of _zeolites_, phillipsite being the most abundant. Their distribution is somewhat wide, but their quantity is slight.

Unfortunately, knowledge of the deep-sea deposits is limited to their superficial layers. Soundings do not usually penetrate more than a few inches, or at most a foot or two.

Unlike shallow-water deposits, those of the really deep sea seem to find no correlatives in the known rock formations of the land.

LAKES.

Most of the phenomena of the ocean are repeated on a smaller scale in lakes. The waves of lakes and their attendant undertows and littoral currents are governed by the same laws and do the same sort of work as the corresponding movements of the ocean. Tides are absent, or insignificant, but slight changes of level, known as _seiches_,[184] have been observed in many lakes. They are probably caused by sudden changes in atmospheric pressure. While they are generally very slight, they frequently amount to as much as a foot, and occasionally to several feet. The seiches are oscillatory movements, and their period is influenced by the length and depth of the lake. They have been studied most carefully in Switzerland. Currents corresponding to those of the ocean are slight or wanting in lakes, but since most lakes have inlets and outlets, their waters are in constant movement toward the latter. In most cases this movement is too slow to be readily noted, or to do effective work either in corrasion or transportation. The work of the ice, on the other hand, is relatively more important in lakes than in the sea.

=Changes taking place in lakes.=—The processes in operation in lakes are easily observed and readily understood. (1) The waves wear the shores, and the material thus derived is transported, assorted, and deposited as in the sea, and all the topographic forms resulting from erosion or deposition along the seacoast are reproduced on their appropriate scale in lakes. (2) Streams bear their burden of gravel, sand, and mud into lakes and leave it there. (3) The winds blow dust and sand into the lakes, and in some places pile the sand up into dunes along the shores. (4) Animals of various sorts live in the lakes, and their shells and bones give rise to deposits comparable to the animal deposits in the sea. (5) Abundant plants grow in the shallow water about the borders of many ponds and lakes, and as they die, their substance accumulates on the bottom. (6) At the outlet the water is constantly lowering its channel. The lowering of the outlet is often slow, especially if the rock be coherent, for the outflowing water is usually clear, and therefore inefficient in corrasive work. These six processes are essentially universal, and all conspire against the perpetuity of the lakes. (7) In lakes where the temperature is low enough for ice to be formed, it crowds on the shores and develops phenomena peculiar to itself. The ice of the sea may work in similar ways, but its work is restricted to high latitudes. (8) In lakes in arid regions, deposits are often made by precipitation from solution. The first five and the last of these processes are filling the basins of the lakes. As the sediment is deposited, a corresponding volume of water is displaced, and, if there be outlets, forced out of the basins; the sixth process is equally antagonistic to the lakes, while the seventh has little influence on their permanence. Given time enough, these processes must bring the history of any lake to an end. The lowering of the outlet will alone accomplish this result if the bottom of the basin is above base-level. Many lakes have already become extinct, either through the filling or draining of their basins, or through both combined. The antagonism of rivers and lakes long ago led to the epigram “Rivers are the mortal enemies of lakes.” True as this statement is, it does not follow that lakes will ever cease to exist, for the causes which produce new lakes may be in operation contemporaneously with those which bring lakes now in existence to an end.

=Lacustrine deposits.=—The beds of sediment deposited in lakes are similar in kind, in structure, and in disposition to beds of sediment laid down in the sea, but river-borne sediment is more commonly concentrated into deltas, since waves and shore-currents are less effective. Even the limestone of the sea has its correlative in some lakes. Some of it was made of the shells of fresh-water animals which throve where the inwash of terrigenous sediment was slight, some of it from the calcareous secretions of plants,[185] and some of it was precipitated from solution.[186] Salt and iron-ore[187] deposits are also sometimes made in lakes.

=Extinct lakes.=—The former existence of lakes where none now exist may be known in various ways. If the lake basin was filled, its former area is a flat, the beds of which bear evidence, in their composition, their structure, and often in their fossil contents, of their origin in standing water. Such a flat is commonly so situated topographically that the basin would be reproduced if the lacustrine deposits were removed. To this general rule there might be exceptions, as where a glacier formed one side of the basin when it was filled. If the lake was destroyed by the reduction of its outlet, or by the removal of some other barrier, such as glacier ice, or by desiccation, shore phenomena, such as beaches, spits, etc., may be found. In time such evidences are destroyed by subaërial erosion, so that they are most distinct soon after the lake becomes extinct.

Many lakes, some of them large[188] and many of them small, are known to have become extinct, while many others are now in their last stages, namely, marshes. Many others have been greatly reduced in size. Such reductions are often obvious where deltas are built into lakes. Thus the delta built by the Rhone into Lake Geneva is several miles in length, and has been lengthened nearly two miles since the time of the Roman occupation. The end of Seneca (N. Y.) lake has been crowded northward some two miles by deposition at its head. Similar changes have taken place and are now in progress in many other lakes.

=Lake ice.=[189]—Since fresh water is densest at 39° Fahr., ice does not commonly form on the surface until the temperature from top to bottom is reduced to this point. Cooled below this temperature, the surface-water fails to sink, and with sufficient reduction freezes. If the lake be small, and especially if it be shallow, it is likely to freeze over completely in any region where the temperature is notably below the freezing-point for fresh water for any considerable period of time. It is under these circumstances that the ice becomes most effective.

Suppose a lake in temperate latitudes, where the range of temperature is considerable, to be frozen over when the temperature is 20° Fahr. If now the temperature be suddenly lowered to -10°, and such change of temperature is not uncommon in the northern part of the United States, the ice contracts notably. In contracting, it either pulls away from the shores or cracks. If the former, the water from which the ice is withdrawn quickly freezes; if the latter, water rises in the cracks and freezes there. In either case, the ice-cover of the lake is again complete. If the temperature now rises to 20° the ice expands. The cover is now too large for the lake, and it must either crowd up on the shores (Fig. 331) or arch up (wrinkle) elsewhere. It follows the one course or the other, or both, according to the resistance offered by the shore.

If the water near the shore is very shallow, the ice freezes to the sand, gravel, and bowlders at the bottom. If the adjacent land is low, the ice in expanding may shove up over it, carrying the débris frozen in its bottom. It may even push up loose gravel and sand in front of its edge if they be present on the shore. Where bowlders are frozen to the bottom of the ice, the shoreward thrust in expanding has the effect of shifting them in the same direction, and even of lifting them a little above the normal water-level. This constant process of concentrating bowlders at the shore-line gives rise to the “walled” lakes, which are not uncommon in the northern part of the United States. The “wall” does not commonly extend entirely around a lake, though it exists at various points on the shores of many lakes. In making the walls, the ice shoved up by winds, especially in the spring when the ice is breaking up, coöperates.

If the lake be bordered by a low marsh, the ice and frozen earth of the latter are really continuous with the ice of the lake, and the push of the latter sometimes arches up the former into distinct anticlines, the frozen part only being involved in the deformation. A succession of colder and less cold periods may give rise to a succession of such anticlines.[190] If the shore be steep and of non-resistant material, the crowding of the ice produces different but not less striking results. Where the thrust of the ice is against a low cliff of yielding material, such as clay, it disturbs all above the shore-line. Where the cliff is sufficiently resistant, it withstands the push of the ice, and the ice itself is warped and broken.

=Saline lakes.=—A few lakes, especially in arid or semi-arid regions, are salt, and others are “bitter.” Beside sodium chloride, salt lakes usually contain magnesium chloride, and magnesium and calcium sulphates. “Bitter” lakes usually contain much sodium carbonate, as well as some sodium chloride and sulphate, and sometimes borax. The degrees of saltness and bitterness vary from freshness on the one hand to saturation on the other. The water of the Caspian Sea (lake) contains, on the average, less salt than that of the sea; that of Great Salt Lake contains about 18%; that of the Dead Sea, about 24%; and that of Lake Van (eastern Turkestan), the densest body of water known, about 33%. See accompanying table.

Many salt lakes, such as the Dead Sea and Great Salt Lake, are descended from fresh-water ancestors, while others, like the Caspian and Aral Seas, are probably isolated portions of the ocean. Lakes of the former class have usually become salt through a decrease in the humidity of the region where they occur. The water begins to be salt when the aridity is such that evaporation from the lake exceeds its inflow. In this case the inflowing waters bring in small amounts of saline and alkaline matter, which is concentrated as evaporation takes place. The concentration may go on until the point of saturation is reached, or until chemical reactions cause precipitation. In general the least soluble minerals are precipitated first. Thus gypsum begins to be deposited from sea-water when 37% of it has been evaporated; but the saturation-point for salt is not reached until 93% of the water has been evaporated (see p. 375). The relations in lakes are similar, and gypsum deposits often underlie those of salt. Deposits of salt and other mineral matters once in solution are making in some salt lakes at the present time, and considerable formations of the same sort have been so made in the past. Buried beneath sediments of other sorts, beds of common salt or of other precipitates are preserved for ages. Lime carbonate has been precipitated in quantity from some extinct lakes (Fig. 333).

The lakes which originate by the isolation of portions of the sea are salt at the outset. If inflow exceeds evaporation, they become fresher and may ultimately become fresh; otherwise they remain salt. If evaporation exceeds inflow they diminish in size and their waters become more and more salt or bitter.

=Indirect effects of lakes.=—Lakes tend to modify the climate of the region where they occur, both by increasing its humidity and by decreasing its range of temperature. They act as reservoirs for surface-waters, and so tend to restrain floods and to promote regularity of stream flow. They purify the waters which enter them by allowing their sediments to settle, and so influence the work and the life of the waters below.

=Composition of lake-waters.=—The accompanying table[191] shows the composition of various inclosed lake-waters, and gives some idea of the wide range, both in kind and quantity, of the mineral matter held in solution by them. It is to be noted that the table shows the composition of the waters of exceptional, rather than common, lakes. The waters of fresh lakes do not depart widely from those of rivers (p. 107).

TABLE—ANALYSES OF THE WATERS OF INCLOSED LAKES.
[+Reduced to Parts per 1000 by Dr. H. J. Van Housen.+]

+----------------+----------------+-----------------+---------------+--------------+
|Locality | Abert Lake, | Bogdo Lake |Caspian Sea. 2°|Caspian Sea, |
| | Oregon | | W. S. W. of | near mouth |
| | | | Pischina, at | of the Volga|
| | | | 15 feet | |
| | | | depth, wind, | |
| | | | W. S. W. | |
|Specific gravity| 1023.17 | | | |
| | | | | |
|Date | May 3, 1883 | | | |
| | | | | |
|Analyst | F. W. Taylor | Gobel | Gobel | H. Rose |
| | | | | |
|Reference |Fourth Ann. Rep.|Lariet Geological|Bischof’s |Bischof’s |
| | U. S. Geol. | Exploration of | Chemical | Chemical |
| | Survey, p. 454| Dead Sea, p. | Geology, Vol.| Geology, |
| | | 284 | I, p. 89 | Vol. I, p. 89|
+----------------+----------------+-----------------+---------------+--------------+
|Sodium, Na | 2.838 | 74.700 | 1.4440 | .3081 |
| | | | | |
|Potassium, K | 10.880 | 1.041 | .0398 | |
| | | | | |
|Rubidium, Rb | | ...... | ...... | ...... |
| | | | | |
|Calcium, Ca | ...... | 3.647 | .1854 | .1238 |
| | | | | |
|Magnesium, Mg | .002 | 13.777 | .4095 | .0728 |
| | | | | |
|Lithium, Li | | | | |
| | | | | |
|Iron, Fe | ...... | ...... | ...... | ...... |
| | | | | |
|Chlorine, Cl | 8.410 | 163.344 | 2.7376 | .4576 |
| | | | | |
|Bromine, Br | ...... | .043 | Trace | ...... |
| | | | | |
|Carbonic acid | | | | |
| gas, CO₂ | 4.653 | ...... | .1382 | .3746 |
| | | | | |
|Sulphuric acid, | | | | |
| H₂SO₄ | .509 | .198 | 1.3372 | .3109 |
| | | | | |
|Phosphoric acid,| | | | |
| HPO₄ | | | | |
| | | | | |
|Nitric acid, | | | | |
| NO₃ | | | | |
| | | | | |
|Boracic acid, | | | | |
| H₃BO₃ | ...... | | | |
| | | | | |
|Silica, SiO₂ | .064 | | | |
| | | | | |
|Alumina, | | | | |
| Al₂O₃ | ...... | | ...... | ...... |
| | | | | |
|Hydrogen in | | | | |
| bicarbonates, H| | | .0023 | .0062 |
| | | | | |
|Ammonium, NH₄ | | ...... | | |
| | | | | |
|Organic matter | ...... | ...... | ...... | ...... |
| +----------------+-----------------+---------------+--------------+
| | 27.357 | 256.750 | 6.2940 | 1.6540 |
+----------------+----------------+-----------------+---------------+--------------+

+-----------------+-----------------+-----------------+-----------------+--------------+--------------+
| Dead Sea, | Dead Sea, near |Dead Sea, at 393 |Dead Sea, at | Elton Lake | Elton Lake |
|Ras Dale, surface| the Island, | ft., between Ras| 656 ft., between| | |
| | surface | Feschkak and | Ras Feschkak | | |
| | | Ras Zerka | and Ras Zerka | | |
| | | | | | |
| 1.0216 | 1.1647 | 1.2225 | 1.2300 | | |
| | | | | | |
| Mar. 20, 1864 | Apr. 7, 1864 | Mar. 15, 1804 | Mar. 15, 1864 | April | August |
| | | | | | |
| Terreil | Terreil | Terreil | Terreil | Gobel | Erdman |
| | | | | | |
|Lartet Geological|Lartet Geological|Lartet Geological|Lartet Geological|Bischof’s |Bischof’s |
| Exploration of | Exploration of | Exploration of | Exploration of | Chemical | Chemical |
| Dead Sea, p. 278| Dead Sea, p. 278| Dead Sea, p. 278| Dead Sea, p. 278| Geology. Vol.| Geology, Vol.|
| | | | | I, p. 403–405| I, p. 403–405|
+-----------------+-----------------+-----------------+-----------------+--------------+--------------+
| .885 | 22.400 | 25.071 | 25.107 | 51.590 | 29.300 |
| | | | | | |
| .474 | 3.547 | 3.990 | 4.503 | 1.162 | |
| | | | | | |
| ...... | ...... | ...... | ...... | | ...... |
| | | | | | |
| 2.150 | 9.094 | 3.704 | 4.218 | ...... | .106 |
| | | | | | |
| 4.197 | 25.529 | 41.306 | 42.006 | 29.971 | 45.598 |
| | | | | | |
| ...... | ...... | ...... | ...... | | |
| | | | | | |
| Trace | Trace | Trace | Trace | ...... | ...... |
| | | | | | |
| 17.628 | 126.521 | 166.340 | 170.425 | 159.498 | 166.890 |
| | | | | | |
| .167 | 4.568 | 4.870 | 4.385 | .059 | ...... |
| | | | | | |
| Trace | Trace | Trace | Trace | ...... | .272 |
| | | | | | |
| .202 | .494 | .451 | .459 | 13.320 | 17.734 |
| | | | | | |
| | | | | | |
| | | | | | |
| | | | | | |
| | | | | | |
| | | | | | |
| ...... | ...... | ...... | ...... | | |
| | | | | | |
| .006 | Trace | Trace | Trace | | |
| | | | | | |
| Trace | Trace | Trace | Trace | | |
| | | | | | |
| ...... | ...... | ...... | ...... | | |
| | | | | | |
| Truce | Trace | Trace | Trace | ...... | ...... |
| | | | | | |
| Trace | Trace | Trace | Trace | Trace | 5.080 |
+-----------------+-----------------+-----------------+-----------------+--------------+--------------+
| 25.709 | 192.153 | 245.732 | 251.103 | 255.600 | 264.980 |
+-----------------+-----------------+-----------------+-----------------+--------------+--------------+

+-----------------+-----------------+-----------------+-----------------+-----------------+--------------+
| Elton Lake | Great Salt Lake | Great Salt Lake | Great Salt Lake | Humboldt[192] Lake| Indevak Lake |
| | | | | | |
| 1.27288 | 1.170 | 2.4 | 1.102 | 1.007 | ...... |
| | | | | | |
| October | 1850 | 1869 | Aug., 1873 | ...... | ....... |
| | | | | | |
| H. Rose | L. D. Gale | O. D. Allen | H. Bassett | O. D. Allen | Gobel |
| | | | | | |
|Bischof’s |Stambury’s |U. S. Geological | Amer. Chemist, |U. S. Geol. Expl.|Lartet Geol. |
| Chemical | Expedition to | Expl. 40th par.| 1874, p. 395 | 40th par. 1877, | Expl. of |
| Geology. Vol. | Great Salt | 1877, Vol. II, | | Vol. I, p. 528 | Dead Sea, |
| I, p. 403–405 | Lake, p. 410 | p. 435 | | | p. 284 |
+-----------------+-----------------+-----------------+-----------------+-----------------+--------------+
| 15.060 | 85.330 | 49.690 | 38.3 | .27842 | 94.050 |
| | | | | | |
| 1.204 | | 2.407 | 9.9 | .06083 | .529 |
| | | | | | |
| | ...... | ...... | ...... | ...... | ...... |
| | | | | | |
| ...... | Trace[196] | .255 | .6 | .01257 | .123 |
| | | | | | |
| 60.540 | .636 | 3.780 | 3.0 | .01648 | 5.076 |
| | | | | | |
| | | Trace | Trace | | |
| | | | | | |
| ...... | ...... | ...... | ...... | ...... | ...... |
| | | | | | |
| 171.936 | 124.454 | 83.946 | 73.6 | .29545 | 158.687 |
| | | | | | |
| | | Trace | | ...... | |
| | | | | | |
| ...... | ...... | ...... | ...... | .20126 | ...... |
| | | | | | |
| 42.560 | 12.400 | 9.858 | 8.8 | .03040 | 3.065 |
| | | | | | |
| | | | | .00069 | |
| | | | | | |
| | | ...... | | ...... | |
| | | | | | |
| | | Trace | | Trace | |
| | | | | | |
| | | ...... | | .03250 | |
| | | | | | |
| | | | | | |
| | | | | | |
| ...... | | | | | |
| | | | | | |
| Trace | ...... | ...... | ...... | ...... | ..... |
+-----------------+-----------------+-----------------+-----------------+-----------------+--------------+
| 291.300 | 222.820 | 149.936 | 134.2 | .92800 | 261.530 |
+-----------------+-----------------+-----------------+-----------------+-----------------+--------------+

+-----------------+-----------------+------------------+-----------------+-----------------+
| Soda Lake, near | Soda Lake, near | Mono Lake, Cal., | Urmiah Lake |Owen’s Lake, Cal.|
| Ragtown, Nev., | Ragtown, Nev., | at 1 foot below | | |
| at 1 foot below |at 100 feet below| surface | | |
| surface | surface | | | |
| | | | | |
| 1.101 | 1.101 | 1.048 | 1.155 | 1.051 |
| | | | | |
| ...... | ...... | July 16, 1883 | ...... | ...... |
| | | | | |
| T. M. Chatard | T. M. Chatard | T. M. Chatard | Hitchcock | O. Loew |
| | | | | |
| Ante, p. 70 | Ante, p. 70 | Bulletin No. 9. |Lartet Geological| Appendix JJ Ann.|
| | |U.S. Geol. Survey,| Exploration of | Rep. Chief |
| | | p. 26 |Dead Sea, p. 284 | Engineers, 1876 |
| | | | | p. 190 |
+-----------------+-----------------+------------------+-----------------+-----------------+
| 41.632 | 40.206 | 18.100 | 74.890 | 21.650 |
| | | | | |
| 2.290 | 2.425 | 1.111 | | 2.751 |
| | | | | |
| | | ...... | ...... | ...... |
| | | | | |
| ...... | ...... | .278 | .529 | Trace |
| | | | | |
| .245 | .245 | .125 | 2.914 | Trace |
| | | | | |
| | ...... | | | Trace |
| | | | | |
| ...... | ...... | ...... | ...... | ...... |
| | | | | |
| 41.496 | 40.206 | 11.610 | 119.496 | 13.440 |
| | | | | |
| ...... | ...... | ...... | | ...... |
| | | | | |
| 15.650[7] | 18.058[7] | 14.465[7] | ...... | 13.140 |
| | | | | |
| 11.771 | 11.943 | 6.520 | 7.671 | 9.362 |
| | | | | |
| | ...... | | | Trace |
| | | | | |
| ...... | ...... | ...... | | Trace |
| | | | | |
| .285 | .287 | .153 | | Trace |
| | | | | |
| .275 | .281 | .268 | | .164 |
| | | | | |
| ...... | | | | Trace |
| | | | | |
| | | | | ...... |
| | | | | |
| | | | | ...... |
| | | | | |
| ...... | ...... | ...... | ...... | Trace |
+-----------------+-----------------+------------------+-----------------+-----------------+
| 113.644 | 113.651 | 49.630 | 205.500 | 60.507 |
+-----------------+-----------------+------------------+-----------------+-----------------+

+----------------+-----------------+-----------------+-----------------+------------------+-----------------+
| | | | | | |
|Pyramid Lake,[193]| Sevier Lake, | Walker Lake,[194] | Winnemucca | Van Lake | Aral Sea |
| Nev. | Utah | Nev. | Lake, Nev. | | |
| | | | | | |
| ...... | ...... | 1.003 | 1.001 | | |
| | | | | | |
| Aug. 1882 | 1872 | Sept., 1882 | Aug., 1882 | | |
| | | | | | |
| F. W. Clarke | O. Loew | F. W. Clarke | F. W. Clarke | Chancourtois | |
| | | | | | |
| _Ante_, pp. 57 |U. S. Survey, W. | _Ante_, p. 70 | _Ante_, p. 63 |Bischof’s Chemical| Roth Chemical |
| and 58 |100 M., Vol. III,| | | Geology, Vol. I, | Geology, p. 465 |
| | p. 144 | | | p. 94 | |
+----------------+-----------------+-----------------+-----------------+------------------+-----------------+
| 1.1796 | 28.840 | .85535 | 1.2970 | 8.502[4] | 2.4512 |
| | | | | | |
| .0733 | | Trace | .0686 | .246 | .0584 |
| | | | | | |
| ...... | ...... | ...... | ...... | | .0022 |
| | | | | | |
| .0089 | .118 | .02215 | .0196 | ...... | .4581 |
| | | | | | |
| .0797 | 2.000 | .03830 | .0173 | .157[4] | .5965 |
| | | | | | |
| | | | | ...... | ..... |
| | | | | | |
| ...... | ...... | ...... | ..... | Trace[197] | .0008 |
| | | | | | |
| 1.4300 | 45.500 | .58375 | 1.6934 | 5.693 | 3.8386 |
| | | | | | |
| ...... | | ...... | ...... | ...... | .0029 |
| | | | | | |
| .4900[7] | ...... | .47445[7] | .3458[198] | 5.267[195] | .0918 |
| | | | | | |
| .1822 | 9.345 | .52000 | .1333 | 2.555 | 3.3368 |
| | | | | | |
| | | ...... | | | .0011 |
| | | | | | |
| | | | | | Trace |
| | | | | | |
| ...... | | ...... | | ...... | ...... |
| | | | | | |
| .0334 | | .00750 | .0275 | .180 | .0032 |
| | | | | | |
| | | | ....... | ...... | ...... |
| | | | | | |
| | | | | | ...... |
| | | | | | |
| | | | | | Trace |
| | | | | | |
| | | | | | Trace |
+----------------+-----------------+-----------------+-----------------+------------------+-----------------+
| 3.4861 | 86.403 | 2.50150 | 3.6025 | 22.600 | 10.8416 |
+----------------+-----------------+-----------------+-----------------+------------------+-----------------+