122 



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

 trust will soon be laid before you. These not only confirm and cor- 

 rect our knowledge of 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. 



4. In Anglesea, Professor Henslow describes* 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 grauwacke. 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 overlying old red- 

 sandstone. 



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

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

 land. 



III. A formation of clay-slate. 



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

 of the Skiddaw region, and composed of chiastolite and hornblende- 

 slates, gneiss, &c, apparently in irregular order. 



V. Granite f. 



* Transactions of the Cambridge Philosophical Society, vol. i. 

 -|- The mineralogical axis of all this tract extends from the centre of the 

 Skiddaw region to the neighbourhood of Egremont. On the north of this 



