Hitchcock.] 64 [December 20, 



form. The most notable example of this which has been observed 

 in our explorations is "Brown's Folly" or Folly hill, a N. W.-S. E. 

 rioVe, one mile long, in the west part of Beverly. The height of 

 these hills varies from forty or fifty feet to one hundred and fifty or 

 two hundred feet above the valleys which separate them, so that they 

 are lenticular masses of glacial drift, or till, fifty to two hundred feet 

 in height, placed here and there, and in many sections very thickly, 

 over the country. 



The material of these hills should be more particularly described 

 as composed of two kinds of till, quite distinct from each other and 

 separated by a definite line, not by gradual transition. The upper 

 member is four or five to fifteen or twenty feet, or sometimes more, in 

 thickness, of comparatively loose, } r ellow or reddish earth with 

 boulders, which are frequently of large size, some of them glaciated 

 but many of them angular and wholly unworn and derived from 

 ledges near by ; the lower member is a very compact, usually blue, 

 stony clay, commonly without large boulders, but with rock-fragments 

 usually abundant up to one or sometimes two feet in size, nearly all 

 of which are glaciated and derived from ledges many miles distant. 

 It will be seen that the upper member is the one almost invariably 

 exposed to view, and this is usually the only one present where only 

 a thin covering of till is found. This material seems to be the con- 

 tents of the great ice-sheet at the time of its final melting, by which 

 it was permitted to fall loosely upon the surface, the yellow or red- 

 dish color arising from change in the iron oxyd under the action of 

 the air. Pressure under the great weight of ice, and seclusion from 

 the air, have caused the very hard and compact character and blue 

 or dark color of the lower member of the till, which is the true 

 ground-moraine. The first of these distinguishing features has caused 

 this portion of the till to be significantly denominated "hard-pan." 

 This constitutes the principal mass of the lenticular hills. 



These hills occur abundantly and conspicuously from Beverly and 

 Danvers through New Hampshire into Maine in a belt ten to fifteen 

 miles wide, near the coast. Inland they are at some places numerous 

 and very well marked, as in Mason, Greenville, New Ipswich, etc., 

 where they occur at heights from nine hundred to eleven hundred 

 feet above the sea. They also occur at East Wilton, and at Aver, 

 Bernardston and Amherst, Mass.; but, in general, over the interior 

 portion of New England these hills are not very frequent. 



