52 SOIL PHYSICS AND MANAGEMENT 



for forming soils depends upon its fineness and the rocks from 

 which it was derived. Many areas known as boulder belts contain 

 so many boulders that it is impossible to cultivate the soil, while 

 in others they were not so abundant but that it is practicable to re- 

 move them. These boulders are sometimes used for making fences, 

 or piled up on waste land (Fig. 47). 



In many cases where the glacier passed over rather soft rocks, 

 such as sandstones or shales, large amounts of this were picked up 

 and pushed along and sometimes formed a very large part of the 

 deposit. The soil formed from it is very inferior. Where the crys- 

 talline rocks, such as granites and syenites, are mixed with lime- 

 stones a very fertile soil results. 



Most of the boulder clay is sufficiently fine for good soils, al- 

 though nearly the entire glaciated area contains some boulders. 

 In the middle west the drift is covered with a layer of fine wind-laid 

 material. 



QUESTIONS 



1. What was the extent of the ice sheet during the glacial period? 



2. To what extent was material deposited ? 



3. What pressure did the ice exert? 



4. How are terminal moraines formed? 



5. Distinguish between kames, eskers, and drumlins. 



6. Name and locate the centers of accumulation in North America and 



Europe. 



7. Tell about the Jerseyan or Nebraskan glaciation. 



8. Give the facts In regard to the Kansan advance. 



9. Tell about the lllinoisan glaciation. 



10. What was characteristic of the lowan? 



11. What was the extent of the Early Wisconsin advance? 



12. What was the extent of the area covered by the Late Wisconsin? 



13. What effect did this have on drainage? 



14. Give some illustrations. 



15. What are boulder belts? 



16. What was the general effect of glaciers on soils? On topography? 



17. What is boulder clay? 



REFERENCES 



1 Levprett, F., Illinois Glacial Lobe, Monograph 38, U. S. Geol. Survey, 

 1899, p. 549. 



General References. Leverett and Taylor. Monograph 53, I'. S. Geol. 

 Survey, The Pleistocene of Indiana and Michigan and the History of the 

 Great*Lakes, 1915, op. Tit. Complete Bibliography, pp. 33-54. Chamberlain 

 and Salisbury, Geology, volume iii. Earth History, The Cause of the Glacial 

 Period, pp. 424-440. Wright, G. F., The Ice Age of North America and Its 

 Bearintr on the Antiquity of Man, New York, 4th ed., 1890, pp. vii-xxv, 

 315-358. 



