168 Professor H, D. Rogers, mi the Geology and [Feb. 8, 



the surface of the continent, comprising two broad continental plains, 

 three great belts of mountains, and two narrow oceanic slopes. 



A. — The largest of these areas is the Great Central Plain, 

 extending from the Gulf of Mexico to the Arctic Sea and Hudson's 

 Bay, and from the Appalachians to the Rocky Mountains, a wide 

 continental region of table-lands, plains, and gentle slopes. 



It consists of two physically different districts — the one a western 

 region of elevated table lands, or steppes; the other, a parallel 

 eastern zone of less average elevation, comprising three great basins 

 or plains, of river and lacustrine drainage. 



I. The Western Steppes. — These constitute a wide zone, east of 

 the Rocky Mountains, about 350 miles broad, ranging from the 28th 

 to beyond the 60th degree of latitude ; including, indeed, the Arctic 

 Highlands, east of Mackenzie River. From the Arkansas to the 

 Upper Missouri this plateau has a mean level above the sea of about 

 4000 feet, rising, at the base of the mountains, to 5000, and at the 

 highest east and west swell of the surface, to 6000 feet. The general 

 eastern boundary of this great terrace, which has a mean height of 

 about 2000 feet, follows approximately the meridian of 98^ W. ; but 

 northward of the Nebraska and Missouri, it is not so well defined. 

 Rising to the foot of the Rocky Mountains, by successive steps and 

 gentle slopes, the plain contains one escarpment, which being much 

 more conspicuous than the rest, seems to divide it into two belts. 

 This, which coincides with the meridian of 101° W., is best marked 

 between lat. 32^ and the Arkansas, but extends to the Forks of the 

 Nebraska, and yet further. From the Pecos to the Nebraska, the 

 upper plateau is about 3500 feet above the sea, and is 1000 feet 

 higher than the table land east of it. This entire western belt, as 

 far north as the Missouri, is a barren and thirsty treeless desert, 

 especially in its southern half. It is without verdure, except along 

 the very attenuated streams, and at certain seasons is entirely rain- 

 less. North of the Missouri it is better irrigated, and more grassy, 

 and includes many rivers and lakes. 



The lower terrace resembles the upper in its flat monotonous 

 surface, its treeless wastes, and arid summer climates, but it is 

 rather more grassy, and its southern streams are better fringed 

 with trees and verdure. All the rivers, from the Pecos to the 

 Arkansas, issue from the upper table land to the lower, through 

 deep narrow sluices (canons), between precipices of enormous 

 height. For more than 400 miles, from the Brazos to the Arkansas, 

 the lower treeless plain is fringed by a remarkable belt of woodland, 

 from 5 to 25 miles wide, which is called the " Cross Timbers." 

 This strip of forest forms the western boundary of the fertile; and 

 better watered still lower plain of Texas, a region of verdant 

 prairies, dotted with natural parks, and clumps of live oaks and other 

 noble trees. 



* II. The Eastern Basins. — This vast tract, embraced between 

 the north-west base of the Appalachian mountains and the eastern 



