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for the thickness of the stratified rocks (177,200 ft.), the time required for their formation, he finds to be 28,000,000 years. Mr. Upham next assumes the thickness of the stratified rocks to be 50 miles, and the rate of land denudation to be one foot in 6000 years. This requires 84,000,000 years for their deposition. Estimates of the relative length of geological time divisions are taken from Dana, Winchell and Davis. Estimating the time since the glacial epoch to be 8000 years, the writer concludes from Davis's ratios, that from 16,000,000 to 40,000,000 years have passed since life first appeared on the globe. From changes in the floras and faunas since the beginning of the tertiary, Mr. Upham thinks the length of Cenozoic time is about 3,000,000 years. Applying this to Dana's and Winchell's ratios, he concludes that about 48,000,000 years have passed since the beginning of Cambrian time. "But," says Mr. Upham, "the diversified types of animal life in the earliest Cambrian faunas surely imply a long antecedent time for their development, on the assumption that the Creator worked before then as during the subsequent ages in the evolution of all living creatures. According to these ratios, therefore, the time needed for the deposition of the earth's stratified rocks and the unfolding of its plant and animal life must be about a hundred million years."

Two-fifths of the earth's area has a mean altitude of-14,000 feet, the plateau of the deep sea; one-fourth the continental plateau a mean altitude of+1,000 feet; the remaining third includes the intermediate slopes, the areas of extreme depth and areas of extreme height. With the exception of the Antarctic continent, the continental plateau is a continuous area, whereas the plateau of the deep sea is "separated by tracts of moderate depth into three great bodies, coinciding approximately with the Pacific, Atlantic and Indian oceans." The author discusses briefly several of the unsolved continental problems. (1) By some it is suggested that the continental form is maintained by the solidity and consequent rigidity of the earth; by others the materials underlying the continental plateau are supposed to be lighter than those beneath the oceanic plateau. The difference in density is the complement of the difference in volume. In the author's view the weight of opinion and the weight of evidence is with the latter hypothesis (the doctrine of isostacy). Accepting this doctrine, the question is (2) whether the difference in density is due to difference in temperature or difference in composition. To this question no answer can be given at present. (3) For the origin of the continents the author mentions Dana's hypothesis that the continental areas cooled first and the oceanic last. Only negative results were obtained by the