Cryptodepressions

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A cryptodepression is part of the earth's crust that lies below mean sea level, the floor of which is hidden (hence, the Greek prefix crypto-) below the waters of a lake. Since the depths of such water bodies are not obtained by ordinary land survey methods and can only be obtained by soundings from a boat, there are numbers of such depressions with only imperfect data, although most lakes are moderately well known. (Note: each of the world's major lakes is treated in detail in separate articles in this volume; see also pr Vol. VI: Hydrology and Limnology). The presence of deep cryptodepressions of great antiquity in the continental crust is an answer to those geologists and geophysicists who claim that the crust has little strength and will everywhere flow (“like wax”). These narrow depressions, forming clefts 2–3 km deep, have clearly remained gaping open for many millions of years. At the temperatures prevailing in the crystalline rocks of the upper cru ...