80 MAX AND THE GLACIAL PERIOD. 



the town of Chelsea, back from the coast into New Hamp- 

 shire, for a distance of twenty-five miles. The base of the 

 ridges does not maintain a uniform level, but the system 

 descends into shallow valleys, and rises over elevations of 

 one hundred to two hundred feet, without interruption. 

 This indifference to slight changes of level is specially 

 noticeable where the system crosses the Merrimac River, 

 just above the city of Lawrence. ' It is also represented in 

 the accompanying plate, where the base of the ridges in 

 the immediate valley of the Shawshin is fifty feet lower 

 than the base of those a short distance to the north, at 

 the points marked «, Z>, and c. The ridges here terminate 

 at the surface in a sharp angle, and are above their base 

 forty-one feet at a, forty-nine feet at b, and ninety-one feet 

 at c. Between c and ~b there is an extensive peat-swamp, 

 filling the depression up to the level of an outlet through 

 which the surplus water has found a passage. 



Several systems of kames approximately parallel to 

 this have been traced out in Massachusetts and New 

 Hampshire, while the remnants of a very extensive sys- 

 tem are found in the OonDecticut Valley above the Mas- 

 sachusetts line. But they abound in greatest profusion 

 in the State of Maine, where Professor George H. Stone 

 has plotted them with much care. The accompanying 

 map gives only an imperfect representation of the ramify- 

 ing systems which he has traced out, and of the extent to 

 which they are independent of the present river-channels. 

 One of the longest of these extends more than one hun- 

 dred miles, crossing the Penobscot River nearly opposite 

 Grand Lake, and terminating in an extensive delta of 

 gravel and sand in Cherryfield, nearly north of Mount 

 Desert. This is represented on our map by the shaded 

 portion west of the Machias River. Locally these ridges 

 are variously designated as " horsebacks," " hogbacks," or 

 " whalebacks," but that in Andover, Mass., was for some 

 reason called " Indian Ridge." Nowhere else in the world 



