ORIGIN OF SOILS 



6g 



the hills and cliffs which it passes. This material consists of all 

 grades of particles, from fine fragments to large pieces of rock. 

 The rock fragments are usually angular, and some of them may 

 be marked with parallel scratches. These scratches are caused by 

 a rock held in the moving ice and pressing against another rock 

 in the earth's crust. 



Fig. 19. Unstratified glacial drift near Chicago. 



At the end of the glacier is deposited a mixture of earth and 

 rocks of all sizes, which is known as a moraine.- When the 

 coming of a higher yearly temperature causes the front of a 

 glacier to retreat, it leaves the surface of the earth covered with 

 the mixed deposit characteristic of glaciers. The deposit beneath 

 the glacier, which is called till, is sometimes an extremely dense, 

 stony clay, having been compacted under the pressure of the 

 moving ice. 



