44 AGRICULTURE. 



times contains great masses of the parent rock 

 which have not been decomposed. By grada- 

 tions the subsoil shades into rotton rock, and 

 from this into solid rock. 



II. Transported Soils. 



The soils upon vast areas of the United 

 States have not been formed from the rock 

 formation which underlies them, but they have 

 been transported thither over long- distances 

 by ice, or water, or wind (Chapter I.). 



1. Drift. Soils deposited by ice are called 

 "drift," and may be distinguished by the pres- 

 ence of boulders. These soils usually consist of a 

 variety of minerals brought together from differ- 

 ent rock formations through the action of 

 glaciers. Drift soils cover great areas in the 

 United States north of the 39th parallel. 



(1) BOULDER CLAY, OR TILL, is the unstratified 

 material which covers the greater part of gla- 

 ciated areas. It is composed partly of preglacial 

 soils and stones pushed before the glaciers, and 

 partly of finely pulverized rock gathered from 

 the bed-rock by the grinding and scraping or 

 the. glacier itself. 



o 



(2) STRATIFIED DRIFT is also found where it 

 has been deposited by the water of glacial 

 streams. 



2. Alluvial Soils are those which have been 

 transported by streams of water (Chapter I.). 

 These are usually stratified, often differing 



