144: HOW ( ROPS FEKD. 



action of moving ice (glaciers) or water (rivers), and de- 

 posited as sediment in their present positions. 



Drift Soils (sometimes called diluvial) are characterized 

 by the following iiarticulars. They consist of fragments 

 whose edges at least have been rounded by friction, if the 

 fragments themselves are not altogether destitute of 

 angles. They are usually deposited without any stratifi- 

 cation or separation of parts. The materials consist of 

 soil proper, mingled with stones of all sizes, fiom sand- 

 granis up to iinmL-nse rock-masses of many tons in weight. 

 This kind of soil is usually disdnguished from all others 

 by the rounded rocks or boulders ("hard heads") it con- 

 tains, which are jiromiscuously scattered through it. 



The "Drift" h:is undoubtedly been formed by moving 

 ice in that period of the earth's history known to geolo- 

 gists as the Glacial Epoch, a perioil when the present sur- 

 face of the country was covered to a great depth by fields 

 of ice. 



In regions like Gi-eenland and the Swiss Alps, which 

 reach above the line of i)erpeLual snow, drift is now ac- 

 cumulating, perfectly similar in character to that of New 

 England, or has been obviously produced by the melting 

 of glaciers, which, in former geological ages and under 

 a colder climate, were continuations on an immense scale 

 of those now in existence. 



A large share of the northern portion of the country 

 from the Arctic regions southward as far as latitude 39°, 

 or nearly to the southern boundaries of Pennsylvania and 

 to the Ohio River, including Canada, New^ England, Long 

 Island, and the States west as far as Iowa, is more or less 

 covered with drift. Comparison of the boulders with the 

 undisturbed rocks of the regions about show that the 

 materials cf the drift have been moved southwards or 

 southeastwards to a distance generally of twenty to forty 

 miles, but sometimes also of sixty or one hundred miles, 

 from where they were detached from their original beds. 



