56 THE PRINCIPLES OF SOIL MANAGEMENT 



in that region when it was formed. In central Michigan, 

 the soil bears scarcely any relation to the underlying 

 rock of the region ; but, in Southern New York and 

 Northern Pennsylvania, the very shaley character of 

 the soil may be traced to the broad area of shale rock 

 which underlies all that section of country, and which 

 was the main source bf the glacial debris. As one passes 

 northward through the finger-lake region of New York, 

 the proportion of limestone and other foreign material 

 resting on the gray shale increases until the exposures 

 of ledge limestone are met at Syracuse and Rochester, 

 portions of which rock had been raked far southward 

 by the ice-movement. This shifting and mingling 

 of material must always be kept in mind in examining 

 glacial soils. 



Purely glacial deposits differ in chemical and physical 

 properties from soils derived from the same formations 

 by other means. There is a large element of mechanical 

 grinding without any large amount of chemical change 

 or solution. The particles have not been subjected to 

 long-continued leaching, which characterizes residual or 

 marine soils. Such material is chiefly rock-flour, that is, 

 pulverized rock. The readily soluble minerals and ele- 

 ments are therefore present in proportionately larger 

 amounts than in soil formed by other means. While a 

 residual soil from limestone may be very poor in lime 

 carbonate, a glacial soil formed from lime-rock is often 

 rich in lime, sometimes containing 50 per cent of that 

 constituent, as has been found in some Dakota soils. As 

 appears from the tables of analyses, such soils are gen- 

 erally rich in all of the basic elements. 



