JEFFERSON COUNTY. 
407 
ceous matter, generally in the form of shining argillite. The mass lies on both sides of the 
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 admitted 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 Loraine. 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 are 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 shall 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 Beverly, Lyndhurst, or in the region of 
the Gannanoqui, it is a repetition of the primary limestones, albitic granite, and the various 
compounds formed by intermixture of the two, and similar in all respects to the rocks of 
Gouverneur, Rossie, 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 
