168 
GEOLOGY OF THE SECOND DISTRICT. 
they had long been considered as the lowest of the transition rocks, and as resting upon the 
primary; and this is unquestionably true in some instances ; but it was not suspected that 
there was a thick mass of sedimentary rocks beneath, abounding in fossils, and filled with 
organic relics. The clearing up of these two points, the mistake in regard to the lower part 
of the Silurian rocks, and the establishment of the fact that they rested not on primary rocks, 
but upon other fossiliferous strata, were real advances in the science. 
Another point which it is proper to speak of in this place, is that which relates to the 
smaller divisions of the rocks. In the Second district, there are several masses which I have 
described as rocks, but still would consider as subordinate ones. In a general treatise, it 
would probably be sufficient so to consider them; but in this report, it appeared essential 
that all those masses which have been or may be employed for important purposes should be 
distinctly noticed and receive a name, inasmuch as they have a place and character by which 
they may be recognized. Thus, the Birdseye limestone, though its name be objectionable, 
yet I have preferred to treat it as a rock, though it may be subordinate to a larger mass of 
limestone. The same may be said of the Black marble of Isle La Motte : it is a thin mass, 
and may be spoken of as a part of the Trenton; yet it is a very important rock, or mass, as 
it furnishes all the black marble of the northern section of the State. The Chazy limestone 
is a much thicker rock than either of the preceding, and appears to be so distinct that it can 
hardly be doubted that it is worthy of a place in the catalogue of New-York rocks. My col¬ 
league, Mr. Vanuxem, however, has grouped the three rocks cited above under one name, 
the Black-river limestone. It appeared then that this fact should be stated, and the matter 
explained, in order to clear up questions which might arise in relation to the three masses, 
Avhich, for the reasons above stated, I have presumed to separate, instead of describing them 
under one appellation. It should be borne in mind, that they may be easily recognized even 
by the lithological characters in most instances, though this character is rarely important 
when applied to any but primary rocks. I have, however, been uniformly disposed to re¬ 
strict the number of New-York rocks ; that is, not to multiply divisions unnecessarily, and 
without cause. We may often find a thick mass in the midst of a formation whose characters 
are somewhat different from those above and below, and yet it will be entirely inexpedient to 
notice this mass as a distinct rock ; and again, as in the case of the black marble in the 
Champlain group, though thin and apparently unimportant, yet it will be found highly use¬ 
ful to notice it as a distinct rock, in consequence of its value in the arts of life. While some 
differences of opinion may exist as it regards individual rocks, there will probably be none 
where the first great division is to be made ; for we do not find it at all convenient to make 
this, till we reach the Medina sandstone. All the rocks below, belong as it were to the era 
characterized by certain forms of life — the Strophomena, Orthis and Atrypa, etc. The 
grades of existence, as found in these oldest of sedimentary rocks of the globe, do not, how¬ 
ever, support and sustain the views of many geologists even of the present day. The gradual 
progression from the low to higher ranks in the scale, do not seem to be borne out by the 
fossils of these lower rocks ; at least not in the positive agreement of fact with theory, as 
has been the custom of some to teach. It is true, that as yet no remains of vertebrate 
