GREY SANDSTONE. 123 



This mass is remarkably persistant ; though its average width is only about ten feet, yet it 

 is found along the Hudson and Lake Champlain, for nearly two hundred miles. It becomes 

 thicker at St. Albans and Swanton, Vermont, and is wrought as a marble, and burned into 

 lime. It is traversed by seams of spar, which often cross the angular fragments of limestone 

 or slate, or even a fossil, under circumstances which demonstrate that the seam was formed 

 subsequent to the formation of the rock by cementation. The fossils arc fragments of the 

 Isotelus gigas, and bivalves belonging to the Trenton limestone. They arc of a date anterior 

 to the formation of the mass, and preexisted in the fragments which compose it. 



The quality of the marble is quite superior, in some respects, to that furnished by the 

 ordinary limestones ; but as its natural joints are obscure, or irregular, it is expensive to 

 quarrj'' ; it being impossible to procure it, except in irregular shaped blocks, which are liable 

 to become shaky, or shattered by the use of gunpowder in raising them from the rjuarry. 



7. Grey Sandstone. 



Termination of the LorrcAn Shales in a Grey Sandstone, in which the number of fossils 

 have diminished. — Characters. — Different masses which appear to belong to the same 

 age. — Termination in a Grey Limestone. 



The Champlain group terminates in a mass which, in Jefferson county, is an even-bedded 

 grey sandstone, whose texture is rather fine than coarse. It is siliceous, but not vitreous. It 

 can scarcely be called a micaceous sandstone, though it is not wanting in any of the layers. 

 The thickness of the beds varies from four inches to two feet. It is colored by the slaty 

 matter diffused through it, and frequently encloses a mass of slate which is similar to that in 

 the Lorrain shales. 



There are no good sections which disclose this rock in connection with the shales below : 

 we see enough, however, to inform us of the changes wliich have taken place in passing from 

 one formation to the other ; they consist simply in a diminution of the green shaly matter, a 

 thickening of tlie beds of sandstone, and the extinction of most of the forms of animal and 

 vegetable life which are so abundant in the rock beneath. 



This rock, in the section of country under consideration, is quite uniform in all its charac- 

 ters ; and it has scarcely been disturbed in its position, or changed by the action of foreign 

 agents, since its deposition. It agrees, therefore, in these respects, with the rocks upon which 

 it rests ; but in order to obtain a full account of the mass which belongs to the period imme- 

 diately subsequent to the Lorrain shales, we are obliged to examine other sections of the 

 State. Though the grey sandstone is much more even-bedded and finer in its materials, and 

 more uniform in its structure, still it appears to be equivalent to what geologists have usually 

 called greyxvacke, in the counties of Columbia, Rensselaer and Washington. The even- 

 bedded fine-grained sandstones are not wanting in the ranges of hills through these counties, 

 yet generally they are coarser, harder and more compacted, and consequently bear some re- 

 semblance to greenstone. It is, however, different in containing beds of breccia ; and though 



