248 



rocks are often violently contorted; while the central system, though 

 cracked and fissured as above described, hardly ever exhibits the in- 

 dications of any flexures. This is explained by the presence of enor- 

 mous unbending masses of compact felspar, porphyrj', &c, which 

 are so intimately associated with the middle division of the slate that 

 the formations cannot be separated. The appearance is explained by 

 referring the felspathic rocks to some modification of sub-marine 

 volcanic action; by supposing that igneous and aqueous causes acted 

 together, and that the operations were many times repeated. 



Srdly. The mean line of bearing of the different systems is shown 

 to be nearly N.E. by E., and S.W. by W. This makes them, one 

 after the other, to abut against the carboniferous zone ; from which 

 it follows that they must also be unconformable to it. The author 

 confirms this inference by referring to detailed sections ; and, from 

 the wholeof the evidence, he concludes, that the central Lake Moun- 

 tains were placed in their present position, — not by a long-con- 

 tinued, but by a sudden movement of elevation, before or during the 

 period of the old red sandstone. 



Lastly, He enters into some details, from which he endeavours 

 to show, that if lines be drawn in the principal bearing of the fol- 

 lowing chains (viz. the southern chain of Scotland from St. Abbs 

 Head to the Mull of Galloway ; the grauwacke chain of the Isle 

 of Man, the slate ranges of the Isle of Anglesea ; the principal grau- 

 wacke" chains of Wales, and the Cornish chain), they will be nearly 

 parallel to each other, and to the line of bearing of the Lake Moun- 

 tains, as above indicated. The elevation of all these chains is referred 

 to the same period ; and the parallelism is not regarded as acci- 

 dental ; but as a confirmation of one of the great principles upon 

 which are founded some of the most beautiful generalizations of the 

 Essays recently published by M. Elie de Beaumont. 



The author next describes the system of faults by which the Lake 

 Mountains were broken off from the central carboniferous chain. 

 After some speculations on the original extent of the carboniferous 

 deposits, which were spread out from the Scotch border to the 

 central plains of England, and perhaps continuous with the similar 

 deposits on the Bristol Channel, he points out some peculiarities of 

 the western coal-fields. 



lstly. The axes of the sevei*al contemporaneous basins are not 

 parallel. 



2ndly. The causes which produced this arrangement appear to 

 have partially affected the then neighbouring grauwacke regions. 

 Thus the transition slate of North Devon does not range parallel 

 to the mean bearing of the grauwacke chain, but to that of the Welsh 

 coal-field. 



Srdly. These coal-fields are contrasted with the carboniferous 

 chain of the north, extending from the latitude of Derby to the 

 mouth of the Tweed : and it is inferred, from the nature of the 

 beds resting on the edges of the dislocated strata, that the eleva- 

 tions of the south-western and northern systems were not perfectly 

 contemporaneous. . 



