1891.] NEW YORK ACADEMY OF SCIENCES, 13 



Dr. Brixton exhibited some Spanish chestnuts in the burr, from 

 a grove in southern New Jersey, and now for sale in the lower part 

 of New York City. 



Prof. Martin spoke of the existence of a fine rocking stone or 

 perched boulder, about ten feet in every dimension, at West Farms, 

 Westchester County, N. Y. ; also of a glacial furrow in Pelham 

 Park. 



Prof. J. F. Kemp then read the following paper, entitled : — 



The Trap Dikes in the Lake Champlain Valley and the 

 neighboring Adirondacks, Illustrated by Numerous Speci- 

 mens and Photographs. 



BY J. F. KEMP, COLUMBIA COLLEGE, AND V. F. MARSTERS, UNIVERSITY 



OP INDIANA. 



(In the preparation of the complete paper of which this article is 

 a condensation, the writers received a little financial assistance from 

 the United States Geological Survey, through Prof. R. Pumpelly, 

 and the thin sections, to the number of 200, were prepared in the 

 laboratory of the Survey. This digest is published with Prof. Pum- 

 pelly's approval. The field-work was done in 1889 and 1890.) 



The shores of Lake Champlain consist in greater part of Cam- 

 brian and Lower Silurian rocks. The extreme southern end is 

 indeed bounded by the ArchiBan; and further north, between Port 

 Henry and Split Rock, and between Willsborough and Port Kent, 

 the foot-hills of the Adirondacks reach and form the water-front, 

 but elsewhere it is chiefly made up of the sandstones, limestones, 

 and shales or slates of the early sedimentary systems. The geolo- 

 gical relations of the latter have been lately elaborated by Messrs. 

 "Walcott, Brainerd, and Seely, but the true succession of the norites, 

 gneisses, and cr3'stalline limestones of the Adirondacks, and even 

 reliable descriptions of their petrographical characters remain to be 

 worked out. The matter hitherto published is but fragmentary, or 

 is based on field observations decidedly incommensurate with the 

 problems involved. 



The whole region is seamed with dikes of igneous rock. These 

 pierce both the crystalline rocks of the Archaean and the sedimentary 

 strata up to and including their youngest member, the Utica slate. 

 On the Vermont side, the most southern dike at all connected with 

 the region is the one lately mentioned by Prof. Pumpelly,' in the 

 Hoosac Mountain, near the Vermont State line, but the most south- 



1 R. Pumpelly. The Relation of Secular Rock- Disintegration, etc. Proc. 

 Geol. See. of America, vol. ii, p. 2U9. 



