526 F. G. CLAPP— GLACIAL PEKIOD IN NEW ENGLAND 



east New England, is 2 to 5 feet (pages 547-548). The Montaiik till in 

 the vicinity of Boston harbor, in Eevere, in the Merrimac vaUcv, and in 

 Maine is, however, perceptibly yellowed to a depth of 15 to 20 feet from 

 the surface, notwithstanding it is far more compact and impervious to 

 percolating waters. This can be well seen in the fine drnmlin sections 

 in Boston harbor and vicinity.* Another good place to observe the 

 weathering in this type of tillis in a cut on the western side of I^ong 

 hill, in West Newbury, Massachusetts, where Merrimac river at some 

 recent date got out of its channel and cut a side valley, now abandoned. 

 The yellowish 'upper portion of the till, here 15 feet deep, is in marked 

 contrast to the blue till below. 



4. Sections showing both this and a more recent till of different char- 

 acter. — The Montauk type of till, while not certainly distinguishal)le 

 from the Wisconsin on the basis of its lithologic characteristics, is gener- 

 ally of a different character. It is in most places hard and tough, con- 

 tains a larger proportion of clay, and is not so loose and gravelly as the 

 Wisconsin type. Plate 57, figure 2, illustrates the general nadire oL' 

 Montauk till, and figure 1 is a sample view of the Wisconsin type oL' till. 



One of the best sections showing both types of till in contact is at 

 Great Boars head, New Hampshire. This is a wave-cut section 15 to 20 

 feet in height, and is well exposed for a length of several hundred feet. 

 The upper 5 to 10 feet is a confused unstratified deposit of till consisting 

 of a mass of boulders 1 to 5 feet in diameter, mixed with some sand. 

 Underlying the deposit and separated from it by a sharp line of deuiarka- 

 tion is a very hard, clayey till, oxidized to a depth of al)out 2 to 5 feet, 

 and containing many boiilders as much as 2 feet in diameter. The lower 

 till is believed to be of Montauk age and the upper till is Wisconsin. 



COARSE GRAVELS 



General description. — Numerous exposures of gravel deposits overlying 

 till are known throughout New England. Many of the gravels are un- 

 doubtedly Wisconsin, but in many places there are extensive gravel de- 

 posits which appear to be of pre- Wisconsin age. These are best exposed 

 in the valleys of Kennebec and Penobscot rivers, in Maine. Tliey consist 

 of unstratified or semi-stratified deposits of coarse gravels composed of 

 fresh pebbles of all sizes and in many sections containing much sand. 

 The sections noted occur along the main valleys and range in thickness 

 up to 100 feet. Their upper surfaces are very irregular and they are 



•W. -O. Crosby: Composition of the till or boulder-clay. Proc. Boston Roc Nat 

 Hist., vol. XXV, 1892, pp. 118, etc. 



