452 Geological Socielt/. 



The general relations of the mountain district of Cumberland had 

 been already briefly but correctly described by Otley *, in a tract 

 to which I have on a former occasion referred. I am now enabled, 

 through the kindness of Professor Sedgwick, to state the general 

 results of iiis own researches in that district, the detail of which I 

 trust will soon be laid before you. These not only correct our 

 information respecting the Cumberland mountains, but determine 

 some of the chief points of analogy which connect them, in structure 

 and composition, with the primary and transition tracts of Wales 

 and Cornwall. 



In Wales, according to Professor Sedgwick, the old red sand- 

 stone seems to pass gradually into the upper members of the fol- 

 lowing series. — 



1. Grauwacke, containing in its upper part organic remains, 

 and graduating into, — 



2. The great slate-formation, containing in all its parts indica- 

 tions of mechanical origin. 



3. A vast group, differing from the ordinary character of the 

 Welsh mountains, in containing a very large proportion of fels- 

 pathose rocks of porphyritic structure. Of this, the mountains of 

 Snowdonia are probably the lowest portion. 



i. In Anglesea, Professor Henslow describes f a still lower group 

 of slaty rocks, including chlorite and mica-slates, and quartz rock; 

 the whole apparently dislocated by — 



5. Protruding masses of granite. 



In Cornwall and Devon, the well known order is — 



a. Grauwacke, with calcareous beds, sometimes containing or- 

 ganized remains. 



b. In two places, a formation of serpentine, which in the Lizard 

 contains diallage-rock, talc-slate, hornblende- and mica-slates, ap- 

 pears to occur beneath the gi'auwacke. Its relations are obscure, 

 but it is superior in position to the following formation. 



c. The great formation of metalliferous-slate (killas); with many 

 subordinate beds of greenstone, felspathic-slate, &c. 



[There is in Cornwall no proper representative of the porphy- 

 ritic formations of Snowdonia (3.)] 



d. Granitic rocks, projecting veins into the incumbent slate ; the 

 granite itself being traversed by other veins of porphyry, called 

 " Elvans." 



In Cumberland, the order is as follows: — 



I. The grauwacke system, containing calcareous beds with or- 

 ganized remains. It is unconformable to the old red sandstone, 

 which rests upon it. 



II. An enormous formation of green-slate, intimately associated 

 with porphyry, like that of Snowdonia, and of Ben-Nevis in Scotland. 



III. A formation of clay-slate. 



IV. A series of crystalline schistose masses ; forming the centre 



* Lonsdale Magazine, for October, 1820. [Mr. Lonsdale's memoir will 

 also be found in Phil. Mag. vol. Ivi. [). 2.57.— Edit.] 



•j- Transactions of the Cambridge Philosophical Society, vol. i. 



of 



