. Biology in America. Biology. 78 Biology in America has both inlet and outlet, its water is being continually changed, and consequently it contains nearly the same amount of salt from year to year. But if a change of climate occurs, sg that evaporation exceeds precipitation, the lake begins to shrink, its outlet is lost and the salts which are carried into the lake by its tributary rivers accumulate, and a little inland sea is formed. Thus have arisen the various salt lakes and inland seas such as the Caspian, the Dead Sea and Great Salt Lake. If now we measure the amount of w^ater carried by
. Biology in America. Biology. 78 Biology in America has both inlet and outlet, its water is being continually changed, and consequently it contains nearly the same amount of salt from year to year. But if a change of climate occurs, sg that evaporation exceeds precipitation, the lake begins to shrink, its outlet is lost and the salts which are carried into the lake by its tributary rivers accumulate, and a little inland sea is formed. Thus have arisen the various salt lakes and inland seas such as the Caspian, the Dead Sea and Great Salt Lake. If now we measure the amount of w^ater carried by the tributary rivers of a closed lake, and determine the amount of salts cai'i-i(^d by them, wo cnii estimate the number of j-ears. Shore op Salton Sea, Showing Old Lake Level ix Background The character of the beaches of extiuct lakes gives a ckie to the weather of the past. After MacDougal. required for the lake to acquire its present degree of saltiness since the time when it had an outlet. Such measurements are at best approximate, due largely to the fact that when rain- fall was greater the rivers carried a greater amount of salt than they do at present, but Avhen compared with the testi- mony of the old shore lines, they furnish a means for determining probably to within 50 or 100 years the periods of heavy and light rainfall in the past. These ancient lake beaches can often be traced for miles with the greatest ease. When a lake maintains the same level for a number of years it leaves an unmistakable record "on the sands" or gravels ''of time" in a clear-cut beach or terrace, where the waves have undermined and cut away the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Young, R. T. (Robert Thompson), b. 1874. Boston, R. G. Badger
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