ESSKX COUNTY. 269 



materials in its way ; or, in other words, forms for itself a channel along the whole line of 

 fracture. 



Just above this rocky chasm the river has two fine falls ; at the lower one it falls into the 

 chasm, and then flows through it with great rapidity and violence, especially during the 

 seasons of high water ; and were not the barriers of the stream composed of the hardest aitd 

 most durable materials, they would long since have been demohshed, at least so far as to 

 give freedom to a turbulent current. 



At the village of Keeseville the sandstone is buried deeply beneath sand and gravel, and it 

 only appears where the river has removed these yielding materials. The rock crops out, some 

 distance above the village, in the banks of the river, but it is exposed only imperfectly. In 

 these exposures 1 found some interesting changes upon the surfaces of some of the layers. 

 One of these presents a smooth and semi-vitreous surface — a kind of glazing. I am at a loss 

 liow to explain this appearance, for 1 have never observed layers whose surfaces resembled 

 this, when composed of sedimentary matter. 



Another kind has projections upon the surface ; that is, the surface is something more than 

 a mere uneven one ; and I can conceive it to have been formed by the dropping or pattering 

 of large drops of water, while the materials were rather soft and yielding, or merely in a 

 semi-indurated state, by which portions of the surface were washed away, leaving the harder 

 parts standing upright. These projections are smooth, and the roughness of the sandstone is 

 thereby somewhat diminished. This surface separates easily from the layer above, leaving 

 in it a mould or cast of itself. If a layer of rock could be heated by applying the necessary 

 agent below^, while the upper part was soft, there would be formed, while drying, a surface 

 like this, especially if sufficiently heated to boil. 



The last kind of surface which some of the layers present at Keeseville, is checked ; a 

 structure evidently produced by the cracking of the layer while drying, the cracks being very 

 similar to those formed in clay exposed to a hot sun. These cracks were subsequently filled 

 by white or greyish siliceous matter, which gives an appearance like that of certain fucoids, 

 particularly the DictuoUtes heckii, in the Medina sandstone. Under some circumstances, 

 they might be mistaken for this fossil. At this place, too, some carbonaceous matter appears 

 in the rock, though no vegetable or animal forms can be distinguished. 



In addition to these diversities in the layers, we fuid them sometimes deeply stained with 

 iron. In the State Collection, the above varieties are represented in the cases which contain 

 the Potsdam sandstone. 



In consequence of this rock presenting two quite distinct varieties, and those varieties being 

 well developed, the one at Potsdam, Si. Lawrence county, and the other at Keeseville, I 

 have sometimes given it a compound name — the Potsdam and Keeseville sandstone ; for the 

 reason that at the former place, a beautiful granular variety exists, and at the latter, a harder 

 and more crystalline mass predominates, which resembles the granular quartz of the Taconic 

 system. 



