Geology and Magnetism, 511 



intersections of the old and new lamina, that the metalliferous de- 

 posits of Ireland are principally found. In the Barony of Bantry 

 the old laminated structure is much contorted and dislocated. 



In North Wales and the northern part of England similar ob- 

 lique intersections of the old and new lamina are observed. The 

 most recent lamination of Cornwall is nearly in the direction of the 

 magnetic needle, and corresponding to that of Wicklow. 



The above observations are not founded merely on a superficial 

 survey of these districts, but on a laborious investigation under 

 ground, as well as on the surface. Indeed, without studying the 

 structure of rocks beneath the surface, where chemical actions are 

 observed in operation, and various crystals constantly forming, 

 it is not possible to arrive at any thing like a correct knowledge of 

 the law which governs the superficies of our globe. 



In Auvergne the laminae of the gneiss and schist run nearly in a 

 direction from south to north, and dip to the west, that is, when 

 viewed on a great scale, for when examined more partially the ordi- 

 nary exceptions occur. In short, the continent of Europe exhibits 

 the uniformity of structure throughout. 



In the United States of America we find the same meridional 

 structure. In Virginia the gneiss, talcose and chlorite slates run 

 north and south, leaning from the perpendicular towards the west. 

 The Boston railway exhibits, by its numerous cuttings in an east 

 and west direction, the general verticality and meridional structure 

 of the schistose rocks for several miles in length. 



Along the north coast of South America, in the Caribbean Sea 

 and the West India Islands, the same structure prevails ; and was 

 minutely examined by the author, from east to west across the three 

 great branches of the Cordilleras, between the latitudes of 4 and 6 

 degrees north. 



In an admirable essay published on this subject by Professor 

 Sedgwick, we find the following observations : — 



" In that variety of slate which is used for roofing, the structure 

 of the rock has been so modified, that the traces of its original 

 deposition are quite obliterated ; and this remark does not apply 

 merely to single quarries, but sometimes to whole mountains. 

 In the Welsh slate-rocks we see the cleavage planes preserving an 



