BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 2, pp. 451-456, PL. 17 APRIL 23, 1891 



ON THE TRIASSIC OF MASSACHUSETTS. 



BY BENJAMIN K. EI\[ERSON. 



[Read before the Society December 31, 1890.) 



CONTENTS. 



Page. 



Introduction 4ol 



Difficulties in the Way of Correlation 451 



The Problem attacked in a new Way 451 



Lithological Distinctions 452 



Structural Relations 45'? 



Currents indicated by the Deposits 452 



The Arkose 452 



The Conglomerate 453 



Buried Peaks 453 



The Sandstone and Shale 454 



Conditions of Deposition 454 



The Monoclinal Faulting 455 



Description of the Map 455 



Introduction. 



DlffiGulties in the Way of Correlation. — The sudden and irregular transi- 

 tions 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 corre- 

 lation 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 I had no longer any 

 hope of finding there the peculiar rocks found among the pebbles of the 

 conglomerates; as my attention was attracted anew to the subject by the 



LXVI-BuLL. Geol. Soc. Am.. Vol. 2, 1890. (451) 



