GENERAL REMARKS. 
167 
rarely intersect each other, or are liable to produce confusion by crossing over the bounds of 
the adjacent groups. This plan, it is true, is the same which is followed in regard to indivi¬ 
dual rocks, viz. giving them local names, according to the place where they may be studied 
to the best advantage; but it is rare that this principle of naming rocks can be followed up 
to so great advantage, as in New-York: the succession is rarely so clear, and certainly the 
combined circumstances can never exist in so favorable conditions to carry out the plan in full, 
as in this State. 
It has been already stated that the rocks of the Second district belong to the lower part of 
the Silurian or New-York system. If we are to rely, however upon the information of foreign 
geologists, and receive without hesitation or examination the classification and divisions 
proposed, we might be in danger of being led astray by authority. In the instance of the lower 
rocks here referred to, we should probably place them in the Cambrian system, provided there 
is sufficient evidence that such a system exists independent of the Silurian. Soon after the 
commencement of the New-York survey, it became necessary to compare the rocks of the 
Second district with those of England; and it soon became evident that some of them be¬ 
longed to the Cambrian system. The slates of the Champlain group, for instance, possessed all 
the characters of the upper members of this system. On comparing these slates, however, with 
those in the northwestern part of the Second district, it was very clear that the only diffe¬ 
rence between them is, that on the east they are disturbed and greatly inclined, while in the 
west they are undisturbed or only slightly inclined to the south. Of the latter rocks, there 
could be but little doubt they were truly a part of the Silurian system of Murchison; at 
least if reliance could be placed upon books, for I had no specimens by which to compare the 
rocks of the two series. The Caradoc division, it was tolerably certain, terminated with the 
Medina sandstone. Now in New-York, the rock immediately beneath this red rock, or red 
marl, in some places is a grey even-grained sandstone, to which succeeds the shales and slates 
which have in some parts at least a strong resemblance to the Llandeilo flags. We, however, 
have not as yet been able to identify them throughout by their fossils : the Asaplius tyrannus 
and huchii have never been found in this country. But however this may be, whether the 
rocks beneath the Medina sandstone are equivalent to the Llandeilo flags or not, they are 
evidently a part of the system of rocks which precede them. There is too much resemblance 
and affinity between those below and those above, to make of them two distinct systems of 
rocks. There is, it is evident, quite a distinct line of difference between the Medina sand¬ 
stone and those below, yet the change is not that which marks a very distinct era in passing 
from one to the other. If then the western shales and slates were silurian, it would follow that 
the eastern division of them is also silurian. It became a question, then, whether this portion 
of the Cambrian had not been mistaken or misunderstood, in consequence of the disturbances 
and changes to which they had been subjected. This was the early conviction which was 
forced upon my mind, and I was led to state this result in the American Magazine, a monthly 
periodical at that time published in this city. Those rocks which have been termed Cambrian, 
have certainly given their full share of trouble to the geologists of both countries. In this. 
