POTSDAM SANDSTONE. 
103 
variety. At those localities where it is strictly a sandstone., it appears to have been formed 
of the debris of granite and gneiss, as, besides quartz, small particles of feldspar, and fine 
scales of mica are disseminated through the mass ; the latter is not, however, very common— 
not so much so as many of the later formed sandstones. The fine-grained hard variety is mostly 
homogeneous throughout, and it rarely presents distinct fragments of feldspar or mica. To 
the eye. it is pure silex; but it probably contains, in intimate combination, particles of both 
feldspar and mica, but ground to extreme fineness. 
It will be necessary to describe two or three other varieties of this rock, which, however, 
appear to be more local than the two varieties already noticed. At the Falls of Montmorenci, 
this rock is stained with carbonate'of copper, which, being intimately mixed with an impure 
earthy portion, gives it the aspect of one of the varieties of the new red sandstone ; and it 
would be very likely to mislead the observer, if seen in almost any other connection. Another 
variety is the white saccharine sandstone, so friable that it is easily crushed in the hand; in 
fact, it forms a pure white sand by disintegration. But a more perplexing variety is found at 
Chazy : it is a calcareous breccia, formed partly of sandstone and fragments of a dirty grey 
calcareous rock; it is an unsightly mass, and comes in near the termination of the rock, or 
at its junction with the calciferous sandrock. In connection with this, there is still another, 
which is a dark iron-brown mass: the particles are rhore angular than' common, and it is 
traversed in all directions with veins of segregation; in detached pieces it would pass for a 
variety of greywacke. In addition to the above, we find very constantly a dark slaty sand¬ 
stone, with impressions of those remarkable relics, called fucoids; it is a mass ten feet thick, 
intervening in some places between the Potsdam sandstone and the calciferous sandrock of 
Eaton. 
From these facts, it will be seen that the termination of this rock is somewhat remarkable. 
In one place, it gradually passes into the calciferous ; in another, the upper layers are brec- 
ciated, forming a very coarse rock ; in another, it passes into an argillaceous sandstone with 
numerous fucoidahimpressions. It is, therefore, clearly distinct from the succeeding rock, 
though some geologists have taken a different view of it, and have been disposed to place the 
calciferous and Potsdam sandstone under one head. 
The lithological description of this rock would be incomplete, were I to omit to notice the 
mass upon the northern, or Canadian slope, where a large proportion of the rock is a conglo¬ 
merate. In most places where the lower mass is in view, it is, as already stated, a conglo¬ 
merate, but it is rarely more than ten feet thick; while upon the Canadian slope, where the 
mass is about three hundred feet thick, it is wholly made up of coarse materials. In addition 
to the preceding, a deep red variety occurs at Chazy: it rests immediately upon the primi¬ 
tive rocks. The typical mass which gives name to the rock, is a very even-bedded sand¬ 
stone ; the beds vary in thickness from two inches to four feet; the planes of deposition arc 
perfectly smooth, and separable from each other. A layer of one hundred square feet of sur¬ 
face may be raised, and afterwards split into rails six inches wide, and ten feet long; or it 
may be broken into pieces of the size of a brick, with even edges of fracture. The color is 
yellowish brown; and when employed for dwellings, it makes an exceedingly neat and com- 
