INVESTIGATION OF TEMPERATURE CHANGES. 249 



from the examination of which Heer has drawn the conchision that, during 

 a part of this epoch at least, the chmate of the region was decidedly tropical 

 in character. The plants discovered and described by Heer indicate that the 

 Cretaceous formation may properly be separated into two divisions, an Upper 

 and a Lower. The vegetation of the Lower Cretaceous is largelj- made up 

 of ferns, coniferous trees and cycads ; the Upper division is distinguished by 

 the presence of dicotyledonous forms. There is evidence that during the 

 lapse of Cretaceous time the climate underwent a change ; but the assem- 

 blage of plants in the Upper division, although less tropical in character than 

 tlie flora of the Lower and earlier portion of the series, is still decidedly one 

 indicating the prevalence of a warm climate during its growth. 



The results obtained by Heer in his examination of the Miocene flora from 

 Atanekerdluk and from otlier localities in West Greenland, and from various 

 points on the eastern coast of that country, as also from Spitzbergen and 

 other places in high northern latitudes, may be justly considered as fur- 

 nishing evidence of the most positive and remarkable character, in regard 

 to the question before us.* Indeed, hardly any geological investigation has 

 ever excited a more general interest than this of the fossil plants of the 

 Arctic regions, since it proves, beyond the possibility of doubt, that the 

 climatic changes on the earth's surface during the later geological epochs 

 have been of the most remarkable character. That a tropical vegetation 

 existed at the North Pole during Cretaceous times was of itself sufficiently 

 astonishing; but when it had to be admitted that, even down to the epoch 

 of the Middle Tertiary, the Arctic regions were covered with the dense forest 

 vegetation of a warm climate, the contrast between the conditions prevailing 

 at that, geologically speaking, not very remote period and those now exist- 

 ino; was too strikino; not to attract universal attention. 



* Hcer's results are publislieil in full in tlie "Flora Fossilis Arctica," and numerous abstracts of them have 

 been given in the scientific journals, as well as in the volumes of travel issued by various e.\:plorers of the Arctic 

 regions. A list of these jiublications will be found in the convenient and carefully edited \'olunie, issued under 

 the auspices of the Goveninient by the Arctic Committee of the Royal Society, for the use of the expedition of 

 1S75 (Manual of the Natural History, Geology, and Physics of Greenland and the neighboring Regions, London, 

 187.T). In the same volume will be found a reprint of Heer's communication to the British Association, at its 

 meeting of 1S66, On the Miocene Flora of North Greenland, and also extracts from the third volume of the " Flora 

 Fossilis Arctica " on the Miocene Flora of the Arctic regions, and a translation of a memoir by the same author 

 on the Cretaceous flora and fauna of Greenland, published in the Memoirs of the Swedish Academy of Sciences, in 

 1S71. From these .sources the statements in the text have been compiled. The climatic results of Heer's investi- 

 gations of the Tertiary flora of Switzerland will be found in the work bearing that name, and also as a sejiarate 

 reprint, under the title of " ITutersuchung iiber das Klima u}id die Vegetationsverhaltnisse des Tertiarlandes," 

 Wintlierthur, 1860. 



