﻿GEOLOGY OF THOUSAND ISLANDS REGION 85 



and are a unity with them also in that, as a rule, they together form 

 a distinct escarpment above the Lowville plateau. In some cases, 

 however, the lowest 2 or 3 feet of the chert beds have remained 

 clinging in very irregular patches to the underlying Lowville, thus 

 forming the serpentine shaped outliers seen in the southern portion 

 of the map. 



The authors, under the necessity of drawing a definite boundary 

 line between the " Black River " and Lowville limestones, which 

 would meet the requirements of being liithologically and faunistic- 

 ally so well marked that it could be mapped with sufficient ease and 

 precision, decided on uniting the cherty beds with the Seven foot 

 tier, the two forming a physiographic and economical unit, as demon^ 

 strated by their being quarried together at Chaumont and other 

 places. Dr Ulrich's investigations had shown him a more com- 

 plete section in Kentucky from which it became apparent that the 

 cherty beds are intimately connected there with the rest of the 

 Lowville and that the unconformity observed in the Watertown 

 region between the cherty beds and the other Lowville represents 

 the hiatus which is filled in Kentucky and elsewhere by beds of 

 transitional character, while on the other hand the cherty beds 

 were found to be also separated by an unconformity from the over- 

 lying beds. Since, moreover, the " Seven foot tier " or Hall's 

 " Black River limestone " is of but local importance, while the Low- 

 ville, including the cherty beds, is a most persistent unit over a very 

 large area, it has been finally deemed preferable by the authors to 

 disregard the local conditions of the Watertown region, and to re- 

 tain the " cherty beds " limestone as a subdivision of the Lowville 

 limestone, under the term " Leray 1 limestone," on account of the 

 typical exposures in the town of Leray. 



The following diagram indicates the relations of the beds as now 

 understood by us : 



" Watertown limestone 

 Black River r Leray limestone member 



group Lowville formation J 



[_ Lowville limestone s. str. 



Since a very irregular surface is observable beween the upper- 

 most tier of cherty beds, about 6 feet thick, and the underlying beds 

 [see section of Klock's quarry, postea p. 90], and this bed contains 

 the cephalopods more frequently than the other cherty beds, Dr 



1 Owing to an error of the printer this word was made to read Leroy 

 on page 72 of Museum Bulletin 138. 



