Scientific Lectures. 95 



tlie Missouri, for liundreds of miles in width, and stretches to the 

 west and southwest, becoming the prevailing color of the map in that 

 direction, and showing a great area occupied by geological forma- 

 tions, newer than the coal. 



The age of these geological foi-mations as determined by their 

 fossils, proves that the entire area occupied by them has been for a 

 long period beneath the waters of the ocean after this part of the 

 continent on which we live had become dry land. We are not yet 

 so familiar with all the clianges that have taken place over this area, 

 that we can indicate, step by step, the process which has at last 

 developed this portion of our continent fi'om the abyss of ocean 

 sediment. The successive formations show the presence of all those 

 which succeed the coal formation in the great geological scale. The 

 New Bed sand stone, or Triassic formation, is succeeded by the Jurassic 

 and this by the Cretaceous and Tertiary. 



It is certain, that in the Cretaceous period, dry land had made its 

 appearance within this western ocean ; for we have abundant evidence 

 of this condition in tlie presence of land plants, distributed over wide 

 areas, and having a great north and south extension, probably 

 parallel with the line of continental elevation. 



During the Tertiary period, it would seem that a great portion of 

 this northern and western area had been elevated above the ocean 

 level, and was occupied by immense lakes of fresh water, which, as 

 the continent rose, gave place to dry land, with a fauna and flora of 

 peculiar character, extending over enormous areas. The vegetation 

 of this period, it is true, was not veiy dissimilar to that of the present 

 in many respects, but it carried many genera of the more temperate 

 latitudes of the present day, far to the northward towards Hudson's 

 Bay, and into Greenland. 



You will perceive, therefore, that this portion of our continent, 

 stretching upon both sides of the great Rocky mountain elevation, 

 and occupying a large extent of the adjacent region, is of very recent 

 origin. The crests of the Rocky mountains, which are of old granitic 

 rocks, may have been islands in this ancient sea, yielding by abrasion, 

 materials to build up the modern formations and the newer conti- 

 nental area. This later addition to our continental area is, as you 

 will observe, not only much larger than the preceding one, and 

 including some portions which may have been islands, is much larger 

 than all the pre-existing area. 



The principal point which I have endeavored to illustrate, is that 



