THIRD REPORT OF THE DIRECTOR I906 33 



was arduous and venturesome, involving risks to person which few 

 would care to take. The results have been entirely satisfactory 

 in solving the general problem above specified. Prof. John H. 

 Cook was placed in charge of the work, having as assistants James 

 F. Loughran, surveyor and Harry C. Cook, photographer. 



The cave-bearing limestones of the Helderberg and Schoharie 

 region are a part of a consecutive series which are geologically 

 classified as follows from below upward: 



At the bottom are the shales of the Hudson River complex, which 

 in the eastern part of the region are unconformable with the beds 

 above. Then follow in ascending order : 



r 



Brayman shale 

 Ontaric or J Cobleskill dolomite 

 Upper Siluric ] Rondout dolomite 

 Manlius limestone 



r Coeymans limestone 

 ^ New Scotland calcareous shale 



Devonic ] 



Becraft limestone 



Above these limestone beds follows a series of sandy and silicious 

 rock strata which are not the locus of caverns. These are: 



( Oriskany quartzite 



^ . -{ Esopus grit 

 Devonic ] c -, ^ • -. 

 [ Schoharie grit, 



all capped by the Onondaga limestone in which again caverns appear. 



The upper terraces and summits of the plateau are constituted of 

 sandstones and shales of Middle Devonic age and are not cavernous. 



Professor Cook has submitted the following preliminary account 

 of his researches. 



In the Siluric and Devonic rocks of Schoharie and Albany coun- 

 ties there are three cavern zones which may be designated as the 

 Onondaga, the Becraft and the Manlius. The first and second are 

 sufficiently characterized by their names but the unbroken suc- 

 cession of lime rock formations between the Coeymans limestone and 

 the Brayman shale (or, where this is absent, the Lorraine beds) 

 must be regarded as a unit and the name Manlius applied to this 

 zone is more or less arbitrary. 



In this investigation it soon became evident that the subsurface 

 drainage is dependent upon the geological structure of the region 



