190 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



niferous deposits on the south, well merit the special attention of 

 the geologist, mineralogist, and chemical philosopher ; for the scale 

 on which these operations of change have been conducted is gigantic. 

 Our present acquaintance with the phaenomena is however sufficient 

 to convince us, that here, as in other countries, the consolidation, 

 rupture, and alteration of large portions of the earth's crust have 

 been effected by the agency and eruption of igneous and gaseous 

 matter." A limestone — ascertained, both by lithological characters 

 and fossiliferous proofs, to belong to the Devonian age, in which 

 copper veins occur at a point where it is intersected in a complicated 

 manner by greenstone porphyry — is converted, for a space 350 

 fathoms long and twenty wide, into a crystalline rock, in some places 

 becoming a pure white crystalline saccharoid marble, and associated 

 with it is a garnet rock, loaded with very beautiful and large crystals ; 

 a case somewhat analogous to that observed by Professor Henslow 

 in Anglesea twenty-five years ago*, and to that in the neighbour- 

 hood of Christiania described by Mr. Lyellf. On the east flank' of 

 the Urals, south of Ekaterinburg, there is a succession of low ridges 

 parallel to the main crest of the chain, composed of metamorphic 

 rocks, some of them so micaceous that they might pass, the authors 

 say, for primary mica-schist ; others resembling gneiss, which a few 

 years ago any geologist would have termed primary, but which are 

 in fact only altered palaeozoic sedimentary strata. 



If we cross the Atlantic to North America, we obtain equally 

 clear proofs of the alteration of the sand and mud of the lands of 

 remote antiquity into crystalline schists, and of the forests that grew 

 upon them into anthracitic coal, by this same powerful agency. 



The Appalachian or Alleghany Mountains, which run from north- 

 north-east to south-south-west for 1000 miles, varying in breadth 

 from 50 to 1 50, and in height from 2000 to 6000 feet, have not, like 

 the Ural chain, the features of a great rent in the earth's crust formed 

 by elastic forces from beneath, and into which molten rocks were in- 

 jected ; they are composed of Silurian, Devonian and carboniferous 

 rocks, in a series of nearly equal and parallel ridges i'ormed by flexures 

 of these rocks. The bending and fracture of the beds is greatest on 

 the north-eastern or Atlantic side of the chain, and the strata become 

 less and less disturbed as they extend westward, until at length they 

 regain their original or horizontal position ; thus offering between 

 the Alleghanies and the western boundary of the basin of the Mis- 

 sissippi a country very similar in conformation to that between the 

 Urals and the Baltic, and composed to a great extent of similar 

 rocks. The internal movements which caused these flexures took 

 place, as in Russia, subsequent to the carboniferous period ; and on 

 the eastern side the igneous rocks have invaded the strata, forming 

 dykes, some of which run for miles parallel to the main direction of 

 the mountains. These igneous rocks are largely developed to the 

 north-east in the States of New Hampshire, Vermont and Maine. 



Near Worcester in Massachusetts, Mr. Lyell observed mica-schist 



* Cambr. Phil. Trans, vol. i. f Elem. of Geol. ii. 403. 



