. FIG. 3—THE IN THE CARBONIFEROUS PERIOD, SHOWING THE POLES. Diagonal Hues denote deep sea ; horizontal lines shallow water: unshaded portions land. Australia drifted into collision with the Sunda islands, with the consequence that an interchange of flora and fauna took place. In seeking an explanation of former climatic condi- tions, geologists have hitherto been averse to the assumption of large movements of the earth's poles with reference to the land. However, the idea that it is necessary to assume a considerable movement of the poles in early Tertiary times has recently been gaini
. FIG. 3—THE IN THE CARBONIFEROUS PERIOD, SHOWING THE POLES. Diagonal Hues denote deep sea ; horizontal lines shallow water: unshaded portions land. Australia drifted into collision with the Sunda islands, with the consequence that an interchange of flora and fauna took place. In seeking an explanation of former climatic condi- tions, geologists have hitherto been averse to the assumption of large movements of the earth's poles with reference to the land. However, the idea that it is necessary to assume a considerable movement of the poles in early Tertiary times has recently been gaining more and more ground. It is impossible to overlook the fact that all former attempts to map out the position of the poles throughout the earth's history come to grief on one obstacle, namely, the Permo- " The dividing line, which defines the extent to which this group has penetrated, has been drawn by Wallace between the islands of Bale and Lombok. continents were grouped concentrically around South Africa, and we thus obtain a connected ice cap of no greater area than that of the quaternary ice-age of America and Europe. Similar, if less striking, simplifications appear when the position of the pole in other geological periods is determined by aid of the displacement theory, and it is not too much to say that this theory makes it possible, for the first time, to determine the former positions of the pole from fossil evidences of climate in a manner that is satisfactory. Finally, the displacement theory may be tested by astronomical determinations of latitude and longitude. It is natural to suppose that the movements are still taking place, and the available estimations of geological time, in spite of their uncertainty, allow us to make an
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