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CONDITIONS OF SEDIMENTARY DEPOSITION.
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ditions under which lime is carried from the land, and to consider how it is distributed in the sea. As was stated early in this paper, the amount of lime carried annually from a given land area is directly related to the efficiency of rock-decay; rock-decay is most efficient over surfaces which have suffered prolonged degradation, and on such surfaces the development of drainage systems has usually resulted in the growth of great rivers. Hence the lime contributed from continents to oceans is delivered chiefly at a few places, the mouths of extended systems, and there is great inequality in the distribution of these along different coasts and among different seas. Of this fact South America is the most conspicuous example, with all its great rivers pouring into the Atlantic, and not one considerable stream entering the Pacific. More limited seas, which receive vast quantities of solutions are the Caribbean and Gulf of Mexico, Arabian Sea, Bay of Bengal and Yellow Sea.

At the mouths of great rivers there exist several conditions which influence the solubility and distribution of lime in the adjacent seas; these are: 1st, the amount of lime in solution in the river water; 2d, chemical reactions between substances in fresh and salt water; 3d, the relative solubility of lime in fresh and salt water; 4th, the conditions of evaporation and agitation of the brackish water; 5th, the effects of currents.

The proportion of solids in solution in a river is dependent not only on the extent and slopes of its basin, but also on the nature of the rocks exposed, and the influence of climate on decay. Under like topographic conditions, silicious schists and a cold climate probably yield a minimum contribution; crystalline rocks and a warm, moist climate yield more; limestone areas, though resistant in a dry climate, suffer most rapid degradation under a humid atmosphere, and the deposits of the later geologic periods, including as they often do quantities of soluble salts, charge the drainage most strongly. The following analyses present specific contrasts, traceable to these geologic and climatic conditions. Each analysis represents but one phase of composition, which varies in each river with high and low

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