Ill 



THE CHEMISTRY OF METAMORPHIC 

 ROCKS. 



(1863.) 



This paper was read before the Dublin Geological Society, April 10, 1863, published 

 in the Dublin Quarterly Journal for July, and reprinted in the Canadian Naturalist 

 for the same year. The notions expressed in the first paragraph as to the exist- 

 ence of crystalline strata of all geological ages, the results of a subsequent alteration 

 of palaeozoic, ineseozoic, and even of cenozoic sediments, are in strict accordance with 

 those which were then (and are even now) maintained by most of the authorities in 

 geology ; and at that time had scarcely been questioned. Hence it is that the rocks 

 of what are here designated the third and fourth series were, in conformity with the 

 conclusions generally accepted, referred to the palaeozoic age. It will, however, be 

 seen that I had at that time no doubt that the rocks of the third (or Green Mountain) 

 series, then regarded as altered Lower Silurian, were, as Macfarlane had already main- 

 tained, the equivalents of a part at least of the Primitive Slate or Urschiefer formation 

 of Norway. He, as is here stated, supposed the Huronian to represent another part 

 of the same formation ; while Bigsby soon after expressed the opinion that the Huro- 

 nian and the Urschiefer are the same. My own extended studies of these rocks in the 

 Green Mountains, in New Brunswick, and on Lakes Superior and Huron, have since 

 convinced me that this view is correct, and that the Green Mountain series is repre- 

 sented in the crystalline strata around the great lakes just mentioned ; and, moreover, 

 that both this series and the crystalline rocks of the fourth or White Mountain series 

 existed in their present crystalline form before the deposition of the oldest Cambrian 

 sediments. The further history of these crystalline series will be found in an Essay 

 on the Geognosy of the Appalachians (XIII. of the present volume), and in its 

 Appendix. In this connection the reader is also referred to portions of those on 

 Granitic Rocks (XL), on Alpine Geology (XIV.), and to the third part of that on Cam- 

 brian and Silurian (XV.). See also a note to the present paper (page 33). 



These conclusions carry back the origin of these two series of crystalline rocks 

 to a much more remote period in geological history than was formerly supposed ; but 

 the chemical principles laid down in this paper I believe to be still true, and of 

 general application, and for this reason it is reprinted with the omission of a few 

 sentences which, by their reference to the supposed palseozoic age of the crystalline 

 rocks above referred to, might serve to mislead the reader. 



While retaining the original title, I however regard the name of metamorphic rocks, 

 as applied to crystalline strata, an unfortunate one, which it would be well to banish 

 from the science of geology. Although it is not to be questioned that local and excep- 

 tional agencies, apparently hydrothermal, have occasionally given rise to crystalline 

 silicated minerals in palaeozoic and even in more recent sediments, and may thus help 



