﻿GEOLOGY OF THOUSAND ISLANDS REGION 91 



on the stoss-seite of the hills. But since the thin limestone slabs 

 over the Trenton belt have been incorporated in great quantities 

 into the drift, whence they have found their way into the stone 

 fences, these stone fences composed of thin Trenton slabs are al- 

 most the most characteristic feature of the Trenton formation in 

 the district and they are remarkably closely bound to the present 

 distribution of the Trenton. 



The contact between the Black River and Trenton groups is but 

 rarely seen, but where found, it indicates an unconformity, either 

 by the irregularity of the contact line, as at the Klock quarry at 

 Watertown, or by the presence of a basal conglomerate bed in the 

 Trenton as at Threemile Bay. 



The best continuous exposure, or in fact the only good one within 

 the boundaries of the mapped area, is that found along a brook at 

 the western outskirts of the village of Threemile Bay [pi. 24, 25]. 

 This section is given below. Another fairly complete section can 

 be obtained from Klock's quarry to the top of Pinnacle hill at 

 Watertown and a third, which however lacks the base, at the west 

 end of Carleton island in the St Lawrence river. 



Section of lower Trenton limestone at Threemile Bay 



(generalized) 

 i6'-if Fine grained thin bedded limestone with shaly intercalations. 

 3' Thin bedded limestone layers with shaly intercalations, rich in 



lamellibranchs, gastropods and cephalopods 

 10' Fine grained black limestone with shaly partings, in part barren, 

 in part full of fossils on shaly partitions, mostly large conical 

 or hemispheric bryozoans (Prasopora simulatrix) in 

 horizon about 2 feet from base 

 3' 6" Black, fine grained limestone full of worm tubes, no other fossils 

 5' 6" Gray, crystalline, thin bedded limestone with many crinoid joints 

 on top (2 feet) and fine grained dark thin bedded limestone 

 below, with shaly intercalations. The limestone beds full of 

 brachiopods (Dalmanella, Rafinesquina) and bryozoans 

 6' Dark gray to black compact limestone^ in strata 1 foot thick with 

 thin shaly partings. Very fossiliferous. Dalmanella 

 testudinaria, Plectambonit'es \ sericeus, 

 Calymmene, bryozoans (Pachydictya a c ul a ) and 

 crinoid joints 

 5" Conglomerate bed with crystalline matrix and crinoid joints 

 Base of Trenton 

 Black River beds 



It follows from this and the other sections that the Trenton 

 begins with a thin conglomeratic bed, on which rest about 6 feet 

 of dark gray to black compact limestone, in beds about 1 foot 

 thick, with thin shaly partings. The latter are very fossiliferous, 

 containing most profusely Dalmanella testudinaria, 

 Plectambonites sericeus, Pachydictya acuta 

 and crinoid joints. 



