288 GEOLOGY OF THE SECOND DISTRICT. 



related to rocks, if they are not really to be considered truly rocks and constituent parts of 

 the earth. It exists again in veins clearly so, but these are found in gneiss. We may notice, 

 in some of them, a disposition to pass into a state of peroxidation. 



Primary limestone occupies an important place in the geology of Essex county. I have 

 regarded this rock as analogous to granite : the wide heavy masses as similar to the wide and 

 extended beds of the ordinary granite, and the narrow vein-like masses as similar to veins of 

 granite in gneiss. The wide beds in both cases are poor in minerals, and the narrow in both 

 cases abound with tliem. In some instances, the narrow veins of limestone contain the same 

 mineral species which have been ejected from volcanoes : thus, the pyroxenes and amphiboles, 

 scapolite and phosphate of lime, idocrase, etc. are more common to thin limestones which 

 occur in a mode similar to that at Long pond, than in the wide and extended masses. 



The sedimentary rocks occupy only an extremely narrow belt along the shore of Lake 

 Champlain ; they exhibit some important facts. They are evidently broken from those rocks 

 which are of the same kind, upon the east side of the lake. The lake lies in a deep rent in 

 the rocks, which has been widened by the action of agents of a different kind. In support 

 of this hypothesis, we find long narrow fissures in the hardest of the rocks, the potsdam sand- 

 stone, for example. The fracture of the rocks themselves, and their dip from the lake or 

 fissures, is proof more positive. 



The tertiary is another remarkable formation. All the facts connected therewith go to prove 

 that it is very recent. Its beds are sometimes slightly disturbed ; but whether from a general 

 uplift, or from having been partially undermined, and a portion in consequence fallen down, 

 cannot be distinctly shown. Hence, it is diflicult to determine the question whether a material 

 change has taken place in particular points since its deposition, or not. The general uplift 

 of the country, since its deposition, must of course be admitted. There is no other rational 

 mode of accounting for the drainage, and the displacement of the ocean, in waters in which 

 this sediment was deposited. 



The igneous or trap rocks never, correctly speaking, form extended masses over the surface 

 of the county, except in one instance, namely, that of the porphyry at Canon's point ; and 

 this is comparatively limited. The trap dykes are far more numerous at the extreme points of 

 the mountain chain, where they terminate upon or near the lake shore, as at Trembleau point, 

 Port Henry, and Split-rock. 



