PALAEONTOLOGY OF NEW-YORK. 
50 
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 
