178 GEOLOGY OF THE SECOND DISTRICT. 



the Hudson has forced a passage through a deep gorge between gneiss on one side, and the 

 Potsdam sandstone on the other, by wiiicli the junction of the rocks is clearly exposed. The 

 fall is occasioned by an uplift, which, as usual, takes place at or near the junction of the two 

 masses. This fact, together with that of the gradual transformation of gneiss into the Pots- 

 dam sandstone, renders this locality an interesting place for examination. Even the partial 

 development of garnet appears in the layers, after the characters of the sandstone are tolerably 

 well formed. This fact is worth bearing in mind, as by it our conclusions may often be 

 modified, and it is the more interesting to myself, perhaps, on account of the application it has 

 to the rocks of the Taconic system ; for should I find in that system a limited extent of mica 

 slate, or an alteration of the granular quartz, by which it approaches granite, I should not 

 conclude that either of those masses are necessarily to be considered as varieties of these two 

 rocks, any more than that the lower layers of the Potsdam sandstone at the High falls are a 

 part of the Primary system. 



At the falls, the sandstone is nearly horizontal, and is about one hundred feet thick. It 

 forms a good building stone, and may be obtained in large flat pieces of any dimensions which 

 may be required. At the locality north and northeast of Glen's-Falls, it is harder, and not so 

 well adapted to the purposes of building. I was unable to find the characteristic fossil, the 

 Lingula , at either of these localities. 



This sandstone, as it exists in Warren, appears adapted to many purposes to which it has 

 been employed in other counties, as an ordinary building stone, and probably for a fire-stone, 

 hearths, furnaces, etc. For the latter purpose, it is much more likely to be found in the 

 vicinity of the High falls, as it is less crystalline, or apparently less changed by proximity to 

 the primary rocks. 



We should expect that a rock so near the primary would often furnish examples of frac- 

 tures and intruded rocks, dykes of greenstone, granite, etc. I have not been able in a single 

 instance, however, to find a dyke traversing this or any of the sedimentary rocks of the 

 county, though they are very common in the primary rocks tliemselves ; there are, in fact, 

 but few instances in the whole district, although they every where approach near to the pri- 

 mary mass. 



A fact attending the formation of this rock in Warren county may be stated, though it is 

 not of much consequence. The lower part is a pure sandstone, to its junction with the pri- 

 mary ; thus, at Corinth, the conglomerate does not exist, but the rock is rather an even- 

 grained sandstone down to its junction with the gneiss over which it lies. The fact appears 

 to show, that wherever conglomerates are formed, they are due to local causes ; and that 

 their period is not properly one which can be termed stormy, as has l^een sometimes inferred. 

 They may, it is true, have been formed in or during a stormy period ; and so they may be 

 entirely local, and formed upon a beach whose waves washed up the coarse materials, or near 

 the mouth of a rapid river which bore along the larger pebbles of its shore. 



The Potsdam sandstone, no where in tiie bounds of this county, is charged with mineral 

 matter, neither disseminated, nor in veins. The only substance which appears in it is iron, 

 which is only in sufficient quantity to give a brownish stain. In an economical point of view, 



