Page:The Journal of geology (IA journalofgeology21894univers).pdf/386

draw his conclusions as he could before the law of homotaxis had been formulated."

Thus, while admitting the possibility of homotaxial relations existing between the floras of widely separated areas, certain correlations, on the basis of simultaneity, of extensive series of beds in different countries, have stood the test of time. On this subject Sir William Dawson has given important evidence.^[1] He says: "I desire, however, under this head, to affirm my conviction that, with reference to the Erian and Carboniferous floras of North America and Europe, the doctrine of 'homotaxis,' as distinct from actual contemporaneity, has no place. The succession of formations in the Palæozoic period evidences a similar series of physical phenomena on the grandest scale throughout the northern hemisphere. The succession of marine animals implies the continuity of the sea-bottoms on which they lived. The headquarters of the Erian flora in North America and Europe must have been in connected or adjoining areas in the North Atlantic. The similarity of the Carboniferous flora on the two sides of the Atlantic, and the great number of identical species, proves a still closer connection in that period. These coincidences are too extensive and too frequently repeated to be the result of any accident of similar sequence at different times, and this more especially as they extend to the more minute differences in the features of each period, as, for instance, the floras of the Lower and Upper Devonian, and Lower, Middle, and Upper Carboniferous."

Turning now from the correlation of strata in widely separated localities, we come to that part of the field in which geology is likely to receive its most valuable aid from paleobotany, viz.: the identification of horizons and their correlation within restricted areas. While the phase of the subject which has just been discussed may be of much importance when the final volume of the geology of the world comes to be written, it can