Abstract

Introduction

Difficulties in the Way of Correlation.—The sudden and irregular transitions from the coarsest to the finest sediments, the derivation of many of the coarse beds from rocks not known in place among the crystallines of the surrounding region, and the prevailing easterly dips have made the correlation and explanation of the Triassic deposits of Massachusetts somewhat uncertain.

They have been explained as in whole or in part of glacial origin; and, by assuming the prevalent easterly dips to represent the true status, a vertical column has been constructed having the following members, beginning with the lowest: (1) Coarse sandstones below the trap; (2) Trap; (3) Sandstones above the trap; (4) The coarse conglomerates of Mount Toby. Thus very improbable thicknesses have been assigned to the series.

The Problem attacked in a new Way.—As my knowledge of the crystalline rocks of the adjoining country became so intimate that . . .

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