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 rehcs. 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 

 hmestone. The same may be said of the Black inarhle 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 lim,estone. 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, 

 which, 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 



