INTRODUCTION. 7S 



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 ai'giiments td 

 show that this metamorphism has not proceeded firom the ddntact or 

 proximity of older granitic or other rocks supposed to be of plutonic 

 origin. The influence of trap-dykes cati have had nothing td 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, df 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 

 MMSSchusetts and the adjacent parts of Vermont, fragments of crinoidal columns, and joints of the 

 same, which preserve the unmistakable structure of these fossils. 



