514 



Report of the State Geologist. 



Black Hirer limestone. The massive dark-colored beds of this rock are 

 well exposed at numerous points in Chazy, directly overlying- the Chazv lime- 

 stone ; but outside of this township it is not well exposed. It has a thickness 

 of thirty to fifty feet and is a brittle, black limestone with conchoidal fracture. 

 ( bfoimnaria aheolata is its most characteristic fossil, but is here confined to a 

 single stratum a few feet thick, at about fifteen feet above the base. Above 

 this is a zone with abundant large Maclureas and large masses of Stromato- 

 cerium, both of which are closely like the corresponding forms in the middle 

 division of the Chazv, so that, unless care is taken, the two may be con- 

 founded, as was done by the writer in one or two instances. On smoothed, 

 mere surface exposures the resemblance is very striking. 



Trenton limestone. In Chazv and Plattsburgh townships are excellent 

 exposures of portions of the Trenton. In the bed of the river just east of 

 Chazy village, 150 feet are exposed lying on the Black river limestone. On 

 Crab island, about 200 feet in thickness is exposed, the larger part of which is 

 above the horizon of the beds at Chazy, while the lower fifty feet corresponds 

 to the upper part of that section. The two together give a thickness of 

 about 300 feet, but the summit is not shown. The faunas are being studied 

 by Mr. T. G. White. In general the lower half is characterized by a. brach- 

 iopod fauna, some bands being crowded with shells of L&ptcena sericea and 

 Orthis. 



The upper one hundred feet of the Crab island section holds a lamelli- 

 branch fauna, with cephalopods and trilobites, while between the two is a 

 zone with a sparse trilobitic fauna. 



This lower portion of the Trenton is mainly made up of black, ringing, 

 somewhat slaty limestone, the different layers presenting much variation in 

 the latter respect. 



In northeastern Plattsburgh, and extending into southeastern Beekmau- 

 town, occurs a series of black, quite slaty, calcareous rocks, which are excel- 

 lently exposed on Cumberland Head. As there exposed they have had 

 developed in them a slaty cleavage at a high angle with the bedding, which 

 has already been described.* In Beekmantown this is not so pronounced, but 

 is present. No base nor summit to these slates is exposed, and the strati- 

 graphic evidence concerning their position is not decisive, but points strongly 

 to their being of Trenton age, or, rather to their not being older than the 

 Trenton. As the Chazy and Crab island sections furnish us with the basal 

 300 feet, and as there is an unknow n vertical interval between the two, these 



•H. P. dishing. Report of New York Stale Geologist for 1MM, vol 1, p. 483. 



