76 Miscellaneous, 



teresting difference of temperature during the Tertiary epocb, in 

 different parts of the North American continent, under the 

 same parallels of latitude. Mr. Lesquereux finds in Dr. Evans's 

 collection of palms, Salisburia^ Cinajnonium, (&c.^ which indicate 

 at least a sub-tropical climate ; a flora quite unlike that from the 

 Miocene of the Upper Missouri, although as he remarks, similar 

 to that of the Miocene of Europe. 



I am tempted to dwell for a moment no the interesting glimp- 

 ses of the physical geography of our continent in geological times 

 which these facts and others that have come under my observation 

 afford. 



\st. A large continental area occupied the place of the interior 

 of North America, from the earliest Palaeozoic ages. 



2d. During the Carboniferous epoch, this land sustained a vege- 

 tation similar to that of the Coal period of Europe and Eastern 

 America, though far less varied. 



Zd. Through theTriassic and Jurassic ages, the sediments from 

 the land were strikingly like, in mineral character, to those of the 

 same age in the Old World : and the flora was characterised by a 

 preponderance of Cycadaceous plants, analogous of those of the 

 Jurassic of Europe. 



4:th. In the Cretaceous age, the central nucleus of the continent 

 was sufficiently extensive to furnish from its ruins arenaceous sed- 

 iments that now cover more than half a million square miles. 

 These sediments contain vast deposits of carbonaceous matter 

 mainly derived from the land plants which covered the continent. 

 As far south as lat. 35® these plants were for the most part Con- 

 iferous or Angiospermous, and included many genera now char- 

 acteristic of temperate climates. 



Through the Tertiary epoch, our continent had nearly the form 

 and area it now has, the Tertiary deposits merely skirting its bor- 

 ders. The Marine Tertiaries are nearly limited to the shores of 

 the present oceans, while the patches of strata of that age found 

 nearer the centre of the continent are all, so far as I have observed 

 or heard, of fresh water or estuary origin. Between the western 

 base of the Sierra Nevada and the Mississippi there are, I believe 

 no Tertiary beds not of this character, and the larger part of 

 the great central plateau has never been covered with Tertiary 

 or Drift sediments, but has, since the close of the Cretaceous 

 epoch, been as now, dry land. 



