Excerpt from Proceedings of the American Philosophical Society, Vol. 61: Held at Philadelphia for Promoting Useful Knowledge, Volume LXI, 1922 It may be remarked parenthetically that I do not consider Aphle biae as indicative of heat, but humidity. That Ginkgo is not a tropical type, but appears to be hardy throughout the Temperate Zone, and does not flourish under cultivation in the Tropics. That Cycads and Conifers are not good criteria for either moist or sub-tropical cli mates, but quite the reverse. That Gleichenia and its present-day segregates, although commonly found in the Equatorial Zone at the present time, are not limited to the tropical part Of that zone, but are frequently more at home in the Sub-tropical or temperate altitudinal zones in Equatorial uplands, as in Hawaii, the Eastern Andes, etc. Doubtless terrestrial plants are better indices of climate than are other organisms, and they are admittedly more important in this respect than marine forms of life. Plant fossils have this merit aside from any question of botanical identification, and this feature seems to have been lost sight of by numerous critics Of paleobotanical prae tise: that the size and form of leaves, their texture, the arrangement and character of their stomata, and the seasonal changes in wood, afford criteria that are quite as valuable climatically even though the species or genus to which they belong remains undetermined. With out venturing further on the sea Of words that constitutes the elusive generalities of most discussions of past climates, I propose to contrast the Tertiary Arctic flora with that which existed contempora neously in lower latitudes, after which I will suggest a possible explanation to account for the observed facts. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.