222 The Western Prairies. 



cases on the lower and in others on the upper silurian strata, over which 

 is spread the drift of the glacial epoch, with its beds of gravel, and boul- 

 ders of granite, from the copper-regions of Lake Superior. As we proceed 

 south over the coal-fields, this band of blue clay thins out, and the drift 

 becomes a friable clay-loam of considerable depth, interspersed in places 

 with thin sheets of sand, in which is found an abundant supply of water, 

 at a depth of ten to thirty feet. In other places, the drift is homogeneous, 

 and wells must be sunk to a great depth. In fact, so variable are these 

 prairies, that each location must be carefully examined before we can de- 

 termine its relative value. 



At one time, this drift may have been of a uniform character ; but by 

 erosion from ocean-currents, and the refilling of these ocean-grooves at a 

 later period, many account for the marked variation in the character of the 

 present surface within short distances. 



We have, along the rivers, alluvium, loess, and drift ; while the great 

 inland prairies are composed of drift from fifty to one hundred and fifty 

 feet in depth. The timber-lands of the small streams are of the same 

 general character. The underlying rock, therefore, has nothing to do 

 with the surface-soil, otherwise than in its deep subterranean drainage. 



The emigrant from the East has little idea of the difiiculties that he 

 must encounter, and looks upon this formation as he would upon the allu- 

 vium of his native rivers, that is composed of the debris of rich rock-soil 

 washed from the hillsides and cultivated fields of the adjacent country. 



In the distribution of rain, different parts of the prairie receive unequal 

 quantities ; and this, too, must be taken into consideration. Add to this, 

 currents of air from the north-west, sweeping down from the polar plains 

 without warning, and the almost steady presence of the damp air-currents 

 coming up from the Gulf of Mexico, which cause new complications that 

 must be taken into account. 



This is the skeleton or framework, the vascular system, upon w^hich we 

 have to build. 



The surface-soil, composed of the remains of plants and insects, is from 

 one to four feet in depth, and almost practically inexhaustible when under 

 very indifferent management. 



While the timber-lands of the East have had their climate changed by 



