.•50 PALiEONTOLOGY OF NEW- YORK. 



the greater masses are made up of the smaller. At the same time 

 we have a partial or entire disappearance of the fauna of a period just 

 in the same ratio of the diminution of the sediments ; unless the con- 

 ditions of life may have been more favorable in some localities. 



We may not forget, also, that in many localities the accumulation of 

 the mass of fifty or one hundred feet, has occupied the same length of 

 time as the mass of one thousand or of five thousand feet ; for the 

 thinning areas of formations show no indication of cessation of depo- 

 sition during any period from their commencement, and we have no 

 evidence that they have not begun and ended as have the entire group 

 in its greater accumulation. 



I have long since shown, from observations in New- York and New- 

 England, that the portion of the Appalachians known as the Green- 

 mountain range is composed of altered sediments of Silurian age ; 

 and the same has been shown by Prof. Rogers to be true of much of 

 the metamorphic part of the range in Pennsylvania. The evidences in 

 regard to the White mountains, though not quite so satisfactory, left no 

 alternative but to regard them as consisting of strata, which, to a great 

 extent, are of newer age than those of the Green mountains, or Devonian 

 and Carboniferous, though fundamentally, perhaps, resting on beds of 

 the same age. The statements of Sir William Logan, in regard to the 

 great accumulation of strata in the peninsula of Gaspe, together with 

 the observations of Prof. Rogers in the Appalachians of Pennsylvania, 

 lead to the inevitable conclusion that the sediments of this age must 

 everywhere contribute largely to the matter forming the metamorphic 

 portion of the Appalachian chain, as well as to the non-metamorphic 

 zone immediately on the west of it. We may then regard it as established 

 that the White mountains owe the great proportion of their mass to 

 sediments of the age of those strata which we have just described, while 

 those of a later period may constitute some considerable portion of the 

 range. 



From the facts here stated, the student is prepared to appreciate the 

 conclusion, that all the sedimentary formations above the Trenton 



