756 KEW YOEK STATE MUSEUM 



island of crystalline rockSj tlie beds are little disturbed and some- 

 times liiglily fossiliferoiTS. The Birdseye rarely exceeds 6 feet 

 in thickness. It is a pure dove colored to dark gray limestone 

 with conchoidal fracture and often containing veins of quartz or 

 calcite. 



The total thickness of the Trenton in the Champlain valley is 

 230 feet, and it overlies the Chazy. Quarries have been opened 

 up at Isle La Motte, Plattsburg, Larrabees point, and Crown 



point. 



The Black river limestone in the Champlain valley is locally 

 known as Isle La Motte marble. It has a varying thickness from 

 35 feet on Larrabees point to 75 feet on Crown point and 20 feet 

 at Plattsburg. The stone is usually heavy bedded, tough, com- 

 pact and black. 



The Trenton proper is exposed at Crown Point (N. Y.) where 

 it has a thickness of 150 feet. It is usually thin bedded and 

 shaly but contains several beds of purer limestone. 



Beginning at a point about one half mile south of Smiths 

 Basin in Washington county, the Trenton limestone extends 

 northward, passing east of ISTorth Granville, east of Whitehall, 

 which lies on the western edge of the belt, then northward in a 

 belt from one mile to half a mile wide, past Benson Landing and 

 northward into Vermont. The town of Yergennes lies on the 

 eastern border of the belt. Another belt of this same rock is 

 found farther south in Y^ashington county, extending from a 

 point half a mile north of Easton Corners up to and for half a 

 mile north of Argyle. Throughout its extent the rocks of these 

 two more or less continuous belts have been highly disturbed by 

 dynamic forces. They are much folded and crushed and at times 

 assume a very slaty structure. The limestone is generally fin© 

 grained and of a black color, is traversed by numerous veins of 

 white calcite and is frequently of high purity. It is mined at 

 Smiths Basin and also west of Pairhaven on the Yermont line. 

 At both of these localities the stone has been quarried for lime- 

 making and flu::. 



