MEDIAEVAL OR MESOZOIC TIMES. 203 



wards, Audubon and Morris explored the same region, and gave 

 details similar to those of Lewis and Clarke. No one, however, has 

 done so much to make known the character and the great extent of 

 this group as Dr. Hayden. Commencing his explorations in 1S54, 

 and continuing them down to the present time, he reduced to order 

 the data which others as well as himself accumulated. Lesquereux, 

 speaking of his work in this field, remarks: " His researches show 

 the constant vigilance and circumspection of a master, attending to 

 the performance of a great work, the building of a monument 

 whose plan has been prepared by serious scientific studies." Hay- 

 den considers that the area of the Lignitic (Laramie) on the Upper 

 Missouri cannot be less than 100,000 square miles, without taking 

 into account the great belt that extends far north from the United 

 States into British America.* Altogether, from British America 

 to the Black Hills, the area covered is not less than 125,000 square 

 miles. Between the Black Hills and the Rocky Mountains, there 

 is still another area of 1,700 square miles. The extent of the 

 soutnern basin, which commences south of Cheyenne and extends 

 to the Colorado plains, east of Denver, and southward to Xew 

 Mexico, has not yet been estimated. 



The most characteristic feature of this group, as already indicated, 

 is the great number of carbonaceous shales and true coal beds 

 which it contains. Fifteen and twenty coal beds sometimes occur 

 in the course of a thousand feet. — (King). Artesian borings at Rock 

 vSprings station in 700 feet brought to light seventeen coal seams, 

 the principal bed being eleven feet thick. Some beds are known 

 and worked that are over thirty feet in thickness. When the great 

 extent of this coal field is considered, it becomes apparent that it is 

 only second in importance to the coal fields of the Carboniferous 

 Age. As is well known, the coal belongs to the series of lignites, 

 and is a superior article. 



Vegetable Life. — The vegetable kingdom had now become clearly 

 modern, the Mesozoic features having passed away. The Flora of 

 this group has been carefully studied by Lesquereux, who has de- 

 scribed from this and the Green River Groups 329 species. This is 

 probably only a fragment of the rich flora of that time, but it is 

 enough to show its general character, and the kind of forests that 

 must have obtained also over the land surface of Nebraska. f In 



*Hayden's Annual lieport for 1874. p. 20. 



tSee Lesquercux's Tertiary Flora, Vol. VII. of U. S. Geological Surveys of the Territories, 

 F. V. Hayden, Geologist. 



