Several systems of kames approximately parallel to this have been traced out in Massachusetts and New Hampshire, while the remnants of a very extensive system are found in the Connecticut Valley above the Massachusetts 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 ramifying 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 hundred 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 are these ridges better developed than in New England, except it be in southern Sweden, where they have long been known and carefully mapped. [Illustration: Fig. 32.--The kames of Maine and southeastern New Hampshire. (Stone.)] The investigations of Mr. W. 0. Crosby upon the composition of till in eastern Massachusetts is sufficiently important in its bearings upon the question of glacial erosion to merit notice at this point.[BA] The object of his investigations was to determine how much of the so-called ground moraine, or till, consisted of material disintegrated by mechanical action, and how much by chemical action. The "residuary clay," which has arisen from chemical decomposition, would properly be attributed to the disintegrating agencies of preglacial times, while the clay, which is strictly mechanical in its origin, remains to represent the true "grist" or "rock flour" of the Glacial period. [Footnote BA: Proceedings of the Boston Society of Natural History, vol. xxv (1890), pp. 115-140.] The results of Mr. Crosby's investigations show that "not more than one-third of the _detritus_ composing the till of the Boston Basin was in existence before the Ice age, and that the remaining two-thirds must be attributed to the mechanical action of the ice-sheet and its accompanying torrents of water. In other words, if we assume the average thickness of the drift as thirty feet, the amount of glacial erosion can scarcely fall below twenty feet. After scraping away the residuary clays and half-decomposed material, the ice-sheet has cut more than an equal depth into the solid rocks."