No. 6.] UPHAM GEOLOGY OF NEW HAMPSHIRE. 327 



or later held in the bottom of the ice, and worn to small size by 

 friction upon the surface over which it moved. The resulting 

 mixture formed beneath the ice is variously called the ground- 

 moraine, boulder-clay, or lower till. It consists of smoothed and 

 striated stones, with fine detritus, which is usually a gravelly 

 clay of dark bluish color, being always clayey, dark, and very 

 hard and compact. The characteristics of the lower till are due 

 to the mode of its formation. Most of its pebbles and boulders 

 are glaciated, having round edges and smoothly worn sides, which 

 often retain striae. These show that the finer material in which 

 they occur has been produced by the slow grinding up of these 

 stones under the ice. The dark and frequently bluish color is due 

 to seclusion from air and water during its formation, as pointed 

 out by Torell, leaving its iron principally in the form of ferrous 

 sulphides, silicates, and carbonates. Its compactness and hard- 

 ness are due to compression under the great weight of ice. 

 Because of this quality, the lower till is commonly known as 

 "hardpan." The same cause has also produced an imperfect 

 cleavage in planes parallel to the surface, noticeable wherever an 

 excavation has been for a short time exposed to the weather. 



While this deposit was thus accumulating beneath the ice, 

 great amounts of material, coarse and fine, were swept away from 

 hill slopes and mountain-sides, and afterwards carried forward in 

 the ice. When this melted, a large portion of the material which 

 it contained fell loosely upon the surface, forming an unstratified 

 deposit of gravelly earth and boulders, which may be called the 

 upjjcr till. In New Hampshire there is almost always a definite 

 line of separation, at a depth varying from two or three feet, as is 

 most common, to fifteen or twenty feet, between the upper and 

 lower till. The upper member is the one usually exposed on the 

 surface, and it is often the only one present where only a thin 

 covering of till is found. Its characteristics are the larger size 

 of its boulders, which are mostly angular and unworn ; the 

 yellowish or reddish color of its fine detritus, produced by the 

 hydrated ferric oxide to which its iron has been changed by 

 exposure to air and water; and the comparative looseness of its 

 whole mass. This division of the till into two members, which 

 is very well marked throughout New Hampshire, is also conspi- 

 cuous in Sweden and other parts of Europe ; and the peculiar 

 features of each have been recently pointed out by Dr. Otto Torell, 

 of Sweden,* in nearly the same terms here used. 



* American Journal of Science and Arts, Third Series, Vol. xiii, p. 77. 



