Reviews 



Climates of Geologic Time. By Charles Schuchert. Carnegie 

 Institution of Washington, Publ. No. 192, pp. 263-98, Figs. 

 87-90. 



There has been a progressive advance, in late years a most rapid 

 one, from the conception of a former hot, dense, vaporous earth atmos- 

 phere, the natural corollary of the Laplacian hypothesis. Knowledge 

 of glacial climates, which had its beginning in studies in the Alps early 

 in the eighteenth century, has grown until not only has there been 

 demonstrated a world-wide lowering of temperature with glaciation of 

 much of the Northern Hemisphere in recent geologic time, but there 

 has been proved as well a number of such glacial periods in earlier 

 times. The cold climates which have periodically affected the earth 

 more or less widely since the beginning of geologic history have been of 

 short geologic duration. The data at hand indicate at least four well- 

 marked glaciations: (1) earliest Proterozoic, shown by the widespread 

 "slate conglomerates" at the base of the Lower Huronian in Canada; 

 (2) latest Proterozoic, marked by thick, widespread tillites beneath the 

 Lower Cambrian of Southern Australia, and by the Gaisa formation of 

 Northern Norway, both now thought to be latest Proterozoic instead of 

 Lower Cambrian; (3) Permian, abundantly proven by tillites in many 

 parts of the world, mostly between latitudes 20 N. and 40°S.; and 

 (4) Pleistocene, the deposits of which mantle much of the Northern 

 Hemisphere. Less well-marked cold periods seem to have occurred (5) at 

 another part of the Proterozoic, for the glacial materials of this age in 

 South Africa represent neither the earlier nor the later part of the era; 

 (6) in the Lower Devonian of • South Africa, shown by the Table 

 Mountain series, and (7) in the early Eocene, indicated by deposits 

 in the San Juan Mountains of Colorado. The greatest reductions of 

 temperatures, so far as known, varied between the hemispheres. 



Guided by the postulate that the living things of sea and land always 

 have been affected by climatic conditions much as now, climate varia- 

 tions are to be observed in the succession of plants and animals recorded 

 as fossils. In addition, the color and general character of the sedimen- 

 tary deposits afford light on climatic conditions at the time of their 



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