JEFFERSON COUNTY. 407 



ceous matter, generally in the form of sliining argillile. The mass lies on both sides of llie 

 river, and forms rocky ridges parallel with it ; at least this is the fact near Albany. From this 

 ridge there is a descent on both sides, terminating in a depression which runs parallel with 

 the river and ridges. Advancing still, we reach another ridge composed of a hard siliceous 

 rock. Now it being proved or adniiltcd that this mass is equivalent to the grey sandstone 

 described above, it would follow that the thickness of the Hudson river shales proper does not 

 much exceed that of the shales of Loraitie. This would therefore take away some of the 

 unexplained points in relation to the Hudson river rocks, and relieve us from the embarrass- 

 ment of maintaining or assuming that they arc twenty or twenty-five miles thick ; for it is rather 

 an assumption, after all, made in consequence of not seeing certain lines of demarcation, 

 where the same mass is repeated over and over again. 



This subject has been remarked upon repeatedly, but it seemed necessary to recall the 

 attention of geologists once more, that this point may be determined. It possesses more than 

 ordinary interest ; for I suspect that some shales present the same facts and anomalies in 

 England and Wales, as in this country. 



Extension of the New-York System in Canada. 



Having stated the leading facts of the geology of the adjacent territory while describing the 

 formation of Lake Champlain, I propose now also to give a brief sketch of the rocks of Ca- 

 nada, those particulaaly near the St. Lawrence river. 



The first remark which I have to make, is, that the rocks of Canada are precisely what 

 ■we should expect, a continuation of those upon the New-York side. The primary rocks of 

 the Thousand islands are confined mostly to those islands ; that is, they do not extend much 

 beyond the opposite shore. At Brockville, gneiss forms a low ridge in the south part of the 

 village ; but to the west and southwest, it is concealed by other rocks. At this place, the 

 sedimentary rock is the potsdam sandstone, or the lower part of the calciferous. Three miles 

 west; we rise one step in the series, and find the upper part of the calciferous well developed. 

 This rock continues twenty-two miles in a southwest direction, or to the head of Plumb valley. 

 It is then succeeded by the potsdam sandstone : this forms a belt of a few miles in width, and 

 then the primary succeeds. 



Without intending to go into particulars or details in an extra-limital survey, I siiall state 

 generally, that in this direction, the rocks of Canada are similar to those of St. Lawrence : 

 first, the sandstone is merely an extension of the potsdam rock ; then the calciferous is also 

 much the same ; and when we reach the primary in Beverl}^, Lyndhurst, or in the region of 

 the Gannanoqui, it is a repetition of the primar}' limestones, albitic granite, and the various 

 compounds formed by intermixture of the two, and similar in. all respects to the rocks of 

 Gouverneur, Rossic, Fowler and Edwards. The similarity extends farther ; the rocks pre- 

 sent the same phenomena in regard to veins and imbedded minerals, so that all the circum- 

 stances relating to the geology of the two regions are identical. But there are some points of 



