No. 543] 



NOTES AND LITERATURE 



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During the later Cretaceous extensive changes took place. 

 The great western mountain chains wore thrown up and com- 

 munication with South America was established ; hut there was 

 a complete separation of the eastern and western land masses. 

 A broad body of water extended without interruption from the 

 Arctic Ocean to the Gulf of Mexico, and the whole of the .meat 

 plains region to the oast of the Rocky .Mountains was then sub- 

 merged. Professor Harshberger believes that this was the per- 

 iod which determined the separation of the Eastern and Western 

 coniferous floras, and the foundation of the great differences in 

 the general floral characters of Atlantic and Pacific North 

 America. 



The Cretaceous is notable in the history of the vegetable king- 

 dom as the time when the highest types of plants first appeared, 

 or at any rate when they are first recognizable. There are no 

 certain evidences of Angiosperms previous to the Sub-Creta- 

 ceous. Apparently' the Cretaceous was a period of great devel- 

 opment of new plant forms, perhaps conditioned by the great 

 changes in the physical character of the continent, these changes 

 undoubtedly causing great changes of climate as well. Harsh- 

 berger thinks that the Cretaceous was probably characterized by 

 periods of mutation — used in the sense of De Vries. Whatever 

 may have been the reason, during the Cretaceous most of the 

 modern angiospermous types, and many of the living genera 

 appeared. The great feature of the later Cretaceous and Ter- 

 tiary forests was the preponderance of dicotyledonous trees and 

 shrubs whose remains are found in great numbers. It is certain 

 that many existing herbaceous genera must also have been 

 present, but with rare exceptions these have not been preserved 

 as recognizable fossils, no doubt owing to their perishable tis- 

 sues which were not fitted to leave fossil remains except under 

 ■'X'-epthmally Favorable conditions. 



The high northern extension of the Cretaceous and Tertiary 

 forests, especially in the Miocene, shown by the fossil deposits 

 as far north as Greenland and Spitzbergen, indicates a relatively 

 warm climate for these higher latitudes of the northern hemi- 

 sphere. Moreover this northern forest belt seems to have been 

 much the same throughout the whole extent of the northern 

 hemisphere, very many species occurring both in the eastern 

 and western hemisphere. Many of the most characteristic of 

 the Miocene genera still exist in America, especially in the great 



