Correspondence — Mr. W. Upham. 283 



COEBESPOUDEUGE. 



THE TILL IN NEW ENGLAND. 



Sir, — Recent explorations of Professor C. H. Hitchcock and the 

 writer in the Geological Survey of New Hampshire show that the 

 unmodified, drift in that State consists commonly of two deposits, 

 quite distinct from each other. These appear to correspond to the 

 lower till and upper till of Scotland and Sweden, described in the 

 second edition of Geikie's Great Ice Age. 



The lower till of New Hampshire and other parts of New England 

 is composed of boulders, gravel, sand, and clay, indiscriminately 

 mingled together, without any traces of stratification such as is pro- 

 duced by currents of water. Most of its pebbles and boulders have 

 their sides planed to flat surfaces, which often retain strise. The 

 detritus in which these are imbedded is usually clayey and dark or 

 bluish in colour, its iron being in an imperfectly oxidized state. 

 This deposit is also distinguished by its being very hard and com- 

 pact, so as to require it to be loosened by a pick before it can be 

 shovelled, which has gained for it among the common people the 

 name of " hard pan." It is the lowest in our series of glacial 

 deposits, and appears by all these features to be the ground-moraine 

 of an ice-sheet. Its accumulation seems to have been by the gradual 

 addition or lodgment of material upon its surface, as is shown by a 

 kind of lamination, which is almost always noticeable in sections 

 that have been for a short time exposed to the weather. The detritus, 

 though filled with rock-fragments, is obscurely divided into flakes 

 one-eighth to one-fourth of an inch thick, which lie in planes parallel 

 to the surface. 



The upper till is a confused mixture of boulders, gravel, and 

 sand, but seldom contains any considerable proportion of clay. It 

 usually shows no stratification of any kind. Its rock-fragments are 

 mainly rough and sharply angular, showing no marks of attrition, 

 and they are generally larger than those in the lower till. Blocks 

 occur in both up to ten feet in diameter, and in the upper till have 

 sometimes from twice to four times that size. The colour of the 

 upper till is yellowish, its iron having been fully oxidized. This 

 deposit is loose, and may be easily excavated. It seems probable 

 from these characteristics that this was material contained in the ice- 

 sheet, gathered into it in its passage over hills and mountains, and 

 that at its final melting the upper till was dropped loosely upon the 

 lower till, or ground-moraine, on which it lies, being separated at a 

 definite line. 



The lower till occurs in flattened or undulating sheets generally 

 throughout New England. It also forms in some districts very 

 remarkable oval hills, which are from a few hundred feet to a mile 

 in length, with two-thirds as great width, while their height corre- 

 spondingly varies from 25 to 200 feet. But whatever may be their 

 size, they are singularly alike in form, having steep sides crowned 

 by a gracefully rounded top, presenting a very smooth and regular 



