Indeed, trains of boulders ought to appear almost everywhere over the glaciated area; and so they do where all the circumstances are favourable. But, readily to identify the train, requires that to furnish the boulders there should be in the line of the ice-movement a projecting mass of rock hard enough to offer considerable resistance to the abrading agency of the ice and characteristic enough in its composition to be readily recognised. Ship Rock, in Peabody, Mass., weighing about eleven hundred tons, and Mohegan Rock, in Montville, Conn., weighing about ten thousand tons, have ordinarily been pointed to as boulders illustrating the power of ice-action. Their glacial character, however, has been challenged from the fact that the variety of granite to which they belong occurs in the neighbourhood, and indeed constitutes the bed-rock upon which they rest.[AV] Some would therefore consider them, like some of which we have already spoken, to be boulders which have originated through the disintegration of great masses of rock, of which these were harder nuclei that have longer resisted the ravages of the tooth of time. It must be admitted that possibly this explanation is correct; but it is scarcely probable that, in a region where there are so many other evidences of glacial action, these boulders could have remained immovable in presence of the onward progress of the ice-current that certainly passed over them. [Footnote AV: Popular Science Monthly, vol. xxxvii, pp. 196-201.] However, as already seen, we are not left to doubt as to the movement of some boulders of great size. That which now claims the reputation of being the largest in New England is in Madison, N. H., and measures thirty by forty by seventy-five feet. This can be traced to ledges of Conway granite, about two miles away.[AW] Many boulders in the vicinity of New Haven, Conn., can be identified, as from well-known trap-dykes, sixteen miles or more to the north. The so-called Judge's Cave, on West Rock, 365 feet above the adjoining valley and weighing a thousand tons, is one of these. Professor Edward Orton[AX] describes a mass of Clinton limestone near Freeport, Warren County, Ohio, as covering an area of three-fourths of an acre, and as sixteen feet in thickness. It overlies glacial clays and gravels, and must have been transported bodily from the elevations containing this rock several miles to the northwest. [Footnote AW: See W. 0. Crosby's paper in Appalachia, vol. vi, pp. 59-70.] [Footnote AX: Geological Survey of Ohio, vol. iii, p. 385,] [Illustration: Fig. 26.--Mohegan Rock.]