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 tliose of England ; and it soon became evident that some of them be- 

 longed to the Cambrian system. The slates of the Champlain gi'oup, 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 httle 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 Asaphus 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 afiimty between those below and those above, to make of them two distinct systems of 

 rocks. There is, it is evident, quite a distinct Hne 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 wliich 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 carnbrian, 

 have certainly given their full share of trouble to the geologists of both countries. In this, 



