EVOLUTION OF THE TERTIARY FLORA IN ASIA

Abstract

ASIA iS a region which has furnished abundant and well-preserved remains of Tertiary plants, which have been described by the best students of palaeobotany, and it is also the region which has preserved in the completest form those communities of plants which inhabited Europe in the earlier and later Tertiary epochs. In the tropical parts of Asia, especially in the Malayan region, are best preserved the plants which flourished in Europe during the Eocene and part of the Oligocene epoch; whereas South-Western China and Japan have preserved the type of vegetation which inhabited Europe and the middle zone of Asia (Western Siberia, Altai, etc.) during the later Tertiary, indeed until the oncoming glaciation destroyed nearly all types of plant life. As is well known, not only did the glaciation put an end to the gradual development of the flora, but mountain chains, already in existence, hindered the free migration of vegetation and prevented the return movement to places where conditions were quite favourable for the existence of the former inhabitants after the ice cover had disappeared. It seems rather strange that the abundance of fossil floras known from Northern Asia failed to suggest of themselves any leading idea regarding the evolution and migration of floras on this great continent. The chief reasons for this failure were that several important floras were confused with others of a different age, and that some were not determined quite correctly. Furthermore, ideas now discarded played a leading part in the discussions. From such causes it followed that certain alien elements were introduced as forming part of floras to which they did not belong, and there resulted a sameness of outlook which prevented further progress and caused some students to reject various palaeobotanical conclusions as unreliable. These results arose chiefly from the inaccuracy of geologists when making their collections. For instance, from I878 until I9I8 (1) Nilssonia serotina was regarded as a Tertiary plant which occurred in Sakhalin so late as the Miocene. Hence even such an authority as A. G. Nathorst was misled into believing that possibly somewhere