180 



GEOLOGY OF THE SECOND DISTRICT. 



But few localities furnish fossils, and the only one of much importance in the Second 

 district is at Chazj-, Clinton county, where the upper part of the rock contains them in great 

 numbers. They will be given when the geology of that county is taken up. 



The order ui wliicli the sedimentary rocks of Warren county occur is exhibited in the sec- 

 tion which extends from Glen's-Falls four and a half or five miles northeast, to the junction 

 of the Potsdam sandstone with the Primary system. 



54. 



a Primary rocks. 

 b Potsdam sandstone. 



c Calciferous sandrock. 

 d Trenton limestone. 



e Black marble. 

 g River. 



In the vicinity of c, two or two and a half miles from the falls, the surface has been deeply 

 abraded and worn, and upon it many primary boulders have been deposited ; beyond this is 

 a great accumulation of sand and boulders, principally of Potsdam sandstone, which have been 

 derived from the mass immediately beneath. In this respect, there is a great uniformity 

 adjacent to all our primary ranges. Near the hue of junction between the two systems of 

 rocks, we find numerous boulders arranged somewhat in regular lines, together with rounded 

 hills composed of sand and gravel. But to return to the consideration of the calciferous 

 sandrock, I remark that its tliickness camiot be well determined at the falls, inasmuch as it 

 is not fully disclosed ; but judging from the presence of the more siliceous layers, it may be 

 estimated at about seventy feet. 



This rock has been extensively quarried for the locks of the canal. It is found to be a 

 durable material for tliis purpose. It has the advantage of other masses belonging to this 

 group, in being a firm thick-bedded rock. It is very tough, and little liable to break ; and 

 such is its texture, that it may be quarried with gunpowder, or receive severe concussions by 

 other means, without producing cracks or flaws. In consequence of its composition, being a 

 mixture of earthy matter with carbonate of lime, it weathers unequally ; the calcareous part 

 being more rapidly acted upon, it leaves the sihceous portion standing out in a rough surface. 

 It has in consequence an unseemly appearance before it is di-essed. 



The mineral substances of this rock appear to be confined to a small quantity of sulphuret 

 of zinc, the particles of which are but little larger than peas ; they are disseminated in the 

 rock, without showing any tendency to form veins. The locality is a mile or two northeast 

 from Glen's-Falls. 



