INTRODUCTION. 
75 
as the mass becomes a homogeneous, crystalline limestone*. And it is 
interesting to observe that while the normal characters of the rocks 
become so completely disguised, and the entire mass is essentially cry¬ 
stalline throughout, there are these indications of the original condition 
in the preservation of fossils. 
At this time it is scarcely necessary to present facts or arguments to 
show that this metamorphism has not proceeded from the contact or 
proximity of older granitic or other rocks supposed to be of plutonic 
origin. The influence of trap-dykes can have had nothing to do with 
producing the change ; and as to a supposed granitic mass or nucleus 
underlying these strata, it exists only in theory, for we have no posi¬ 
tive and tangible evidence of such a nucleus. It is true that in the 
Appalachian chain there are masses and even considerable areas 
of what is termed eruptive or intrusive granite.; but the existence of 
such granite furnishes no evidence that it is derived from a primary 
mass, or that it has been erupted in a state of igneous fusion. Such 
masses of granite may, indeed, and very probably have been derived 
from the formation immediately beneath the one on which it rests; and 
it is almost certainly in all cases a modification of some pre-existing sedi¬ 
mentary rock. We are well aware that the Laurentian mountains of 
Canada, and the mountains of the same age in Northern New-York, 
are metamorphosed sedimentary strata; and we have to look for the 
intervention of some of the thinning strata of these formations beneath 
the Appalachians, before we reach the hypothetical plutonic mass 
below. 
Perhaps there is no fact of more interest and significance in connec¬ 
tion with these older long designated primary formations of the Lau¬ 
rentian range, than the discovery of Sir William Logan that these 
crystalline masses do enclose fragments of pre-existing stratified 
rocks; these fragments still retaining the original lines of lamination. 
* It is not uncommon to find upon the weathered surfaces of the crystalline limestones, in Western 
Massachusetts and the adjacent parts of Vermont, fragments of crinoidal columns, and joints of the 
same, which preserve the unmistakable structure of these fossils. 
