56 GEOLOGY. 
The remains of organisms are somewhat more distinct in No. 6, but even these are too much 
changed to be satisfactorily determined. 
The lithological character of this group is much like that of some of the Chemung rocks; but 
the corals, as they seem to be, which make up so much of the mass of the limestone bands in 
their abundance and general appearance, resemble more the intermingled branches of Chaetetes 
which cover the surfaces of some of the Silurian strata, than any fossils of later date. 
o. T is a very dense and massive limestone, of a light blue or gray color, everywhere pene- 
trated by lines of deep red. This character is common to several bands of limestone in the 
series, and distinguishes them from any I have ever seen elsewhere. The same appearance 
would be produced if the stems of corals, sometimes so abundantly distributed through the 
Devonian and Silurian limestones, were impregnated with oxide of iron. All the limestones 
below No. 1 contain considerable silica, and have doubtless been affected by the silicious infil- 
tration to which I have already referred. 
The foliated sandstones of No. 10 have an indescribable look of antiquity. They are usually 
fine grained and hard, the lighter ones drab or gray, specked with dark red. The shales above 
and below these sandstones are very soft, red, or green mudstones, containing great numbers 
of cylindrical bodies, which resemble the casts of worm holes. 
Nos. 12 and 13 are coarse silicious rocks, having the same appearance of extreme age as No. 
10, but much coarser and more massive. The lithological characters of these strata are 
strikingly like those of much of the Potsdam sandstone in the exposures I have examined of 
that rock.on Lake Superior and in Canada. 
The color of the upper division is a light yellowish brown, sometimes nearly white; of the 
lower portion, dark red and purple. In some parts of the sections, especially near the base, 
the light and dark colors are united in narrow stripes ; and as this portion of the rock is ex- 
ceedingly compact and fine-grained, it occasionally resembles a striped, purple and white 
jasper. These sandstones, as will be seen in the specimens collected, are apparently somewhat 
metamorphosed, portions of them being harder and more crystalline than any unchanged sedi- 
mentary rock that I remember to have seen; but the perfect harmony of stratification every- 
where prevailing, as well as the evident antiquity of all the irregularities of the underlying 
granite, around which the strata of sandstone are now resting just as when so quietly depos- 
ited, lead me to infer that their consolidation is not due in any degree to volcanic heat, but 
rather to molecular changes induced by the long-continued pressure of the immense mass of 
superincumbent rocks. When it is remembered that every square foot of the basal structure 
of the table lands has sustained a great and constantly increasing pressure from the earliest 
palzozoic times, and that since the deposition of the Chalk, that pressure has been at least 
500,000 pounds on every square foot, this cause alone will probably be considered quite ade- 
quate to produce the degree of metamorphosis exhibited by the strata under consideration. 
In the absence of fossils, whatever conclusions may be arrived at in regard to the age of 
these sandstones must be in some degree conjectural and liable to modification by the discov- 
ery of new facts ; yet the evidence is in a good degree satisfactory that they are the equiva- 
lent of the Potsdam sandstone of the New York geologists. 
The indications of this identity are found in their great relative antiquity and in their litho- 
logical characters. From the limestone called Lower Carboniferous b y Mr. Marcou, they are sep- 
arated by over 3,000 feet of sedimentary strata ; and from what I have considered the base of 
the carboniferous series, by nearly 2,000 feet. 
_ The question of their age, then, resolves itself into this: Are they Devonian or Silurian? 
They are not so remote from the Carboniferous rocks but that, reasoning from the thickness of 
the Devonian strata in other parts of the world, we might perhaps include them in that for- 
mation; but while in New York the Devonian rocks are several thousand feet in thickness, they 
