CHAZY LIMESTONE. 



273 



Limestone in shaly masses, four feet ; stratum of compact limestone, two feet ; concretionary limestone, 

 fifteen inches ; limestone stratum, six inches ; shaly limestone, two feet ; very compact limestone, twelve 

 inches ; slaty limestone, six inches. Tough compact limestone ; containing Maclurea magna seven inches 

 in diameter, occupied the rest of the way to the water's edge (a few inches.) This is not the bottom of the 

 chazy limestone, as the same fossils are found at Point au Eoche, N. Y., west of Isle La Motte, with an 

 easterly dip. 



Filk',. 



Fleury's. 



FIG. 172. 



JJiWs south. 



Coarse G. limestone. 



Jtfrtck marble. 



Trent, 



Section of Cbazy Limestone across Isle La Motte. 



Fig. 172 represents a section of the Chazy limestone upon this island, overlaid by Trenton limestone. The 

 position of the different quarries is indicated by gaps in the section, and the overlying strata of Trenton 

 limestone are next above the heavy black line on the right hand of the section. The section runs in a 

 northeast and southwest direction across the upper part of the island. A map of this island is given in 

 Plate VIII, Fig. 3, and a description of it will presently be oifered. 



We will add a few words respecting some of these lithological characters. The chert, 

 abundant in the second variety, is very prominent near Basin Harbor in Ferrisburgh. 

 The chert being harder than the limestone is not so easily decomposed ; and hence it 

 appears in irregular forms, sometimes drawn out into long curls, projecting along the line 

 of strike. They are thus seen to be confined to particular layers. This chest and a few 

 grains of sand are all the silicious matter contained in this group in Vermont, while else- 

 where, as in Canada, strata of sandstone, like the Potsdam, are said to occur. It is not 

 unlikely that the cherty masses indicate the former presence of fossils, and in some 

 bunches a coralline structure is still evident. The brown earthy spots and geodes of 

 quartz and calcite, found in the rock below, are entirely wanting in this rock. 



The third variety encrinal limestone is designed to specify a red mass of encrinital 

 stems found below Fisk's quarry on Isle La Motte, where it was discovered by Prof. 

 Thompson. It is red and white, and much resembles the beautiful encrinal limestone of 

 Lockport, N. Y. Large bowlders of this variety are found in the north part of North 

 Hero, which probably originated from this locality. We have noticed this variety no 

 where else. The stratum is nearly three feet thick. The specimens of it in the Cabinet 

 are NOB. 539, ^o anc * * 



We have noticed the concretionary variety at several localities, particularly at the 

 south end of Isle La Motte, and in the west part of Panton. The concretions vary in 

 size from a pin's head to spherical masses from one to two inches in diameter. Some are 

 spherical, others are elongated. All resemble small pebbles, and it was only a careful 

 examination that showed us that this variety, in some of its forms was not a sandstone 

 cemented by carbonate of lime. They are Nos. jfg to jfg. 



Specimens of brecciated limestone belonging to this rock occur in the west parts of 

 Ferrisburgh and Panton. It may be regarded as a conglomerate, formed from the ruins 

 of the calciferous sandrock. The fragments are occasionally rounded. 



At the south end of Isle La Motte, there are a great abundance of shrinkage cracks or 

 sun cracks. They were mud veins, originally, upon the shore of the silurian ocean, filling 

 the cracks caused by the rapid drying of the mud by a tropical sun. More or less 



