Abstract

Evidences of orogenic Action.

More than once I have called attention to the fact that the Tertiary and Cretaceous beds on the island of Marthas Vineyard, Massachusetts, show throughout an area of about fifty square miles unmistakable evidence of mountain-building stresses. The strata, having an aggregate thickness of certainly many hundred, perhaps of some thousand feet, have been thrown into folds of considerable amplitude, which are so sharply compressed that the numerous outcrops show dips which average more than 45°. The suggestion that these distortions have been produced by the shearing action of the ice in the last glacial period is completely disproved by the very well developed preglacial topography which this region exhibits—contours of hill and dale which were formed in these soft rocks after they were folded, and on which the drift rests as an incomplete mantle. It is impossible to conceive that the folding of the . . .

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