1823.] Geological Tvansattions of Cornwall^ Vol. II, 47 



The local details of which this paper consists are not suscep- 

 tible of abridgment ; but it contains the following analysis of the 

 serpentine of Clickertor, by the late Mr. Gregor, which, we 

 believe, has not hitherto been giveji to the public : 



Silex. ......•.•...,..,,,.,,,. 42-2 



Oxide of iron ,••...,... ^ ^ ... ^ j ^ 1 ♦ , . . 19*6 



Magnesia. 'v^'i^,'^ r « *-i*.» -f 16*0 



Alumina ,^ . , , '.> , , ... . / 2*2 



Lime 0*8 



Water 11-4 



i'i;*\r^nt 



m 



92-2 



X. On the Phenomena of Intersected Lodes, and the legitimate 

 Inferences which may he drawn from them ; and 



XI. On the Intersection of Lodes in the Direction of their Dip 

 or Underlie. By John Hawkins, Esq. FRS. &c. Hon. MGSC. 



These interesting papers cannot usefully be epitomized. 



XII. On the Geology of the Land's End District. By John 

 Forbes, MD. Hon. Mem. and late Sec. GSC. 



We have only room for a brief general sketch of the subject of 

 this memoir, — the physical structure of that portion of Cornwall 

 situated to the westward of a . line drawn from the estuary of 

 liayle, on the north coast, to Cuddan Point on the south, which 

 Dr. Forbes calls, for the sake of distinction, the Land's End 

 district. " The geological structure of this district," he 

 observes, " may be said to be very simple, inasmuch as it 

 includes but a small number of rocks, and as the various rela- 

 tions of these to each other are very similar and readily disco- 

 verable. The main body of the district is granite, — a rock which 

 indeed constitutes nine-tenths of the whole. On the edges of 

 the granite, in different points of the coast, reposes a certain 

 assemblage of rocks, which, from their intimate relations, ob- 

 viously constitute owe /or//ztf^/ow. These rocks I shall take the 

 liberty of naming in this paper the slate formation ; a term which 

 answers exactly to the killas country of the miners and farmers 

 in this part of the county. Generally speaking then, this dis- 

 trict consists of two, and only two formations ; the granite fornix 

 ation, and the slate formation ; very dissimilar in appearance, 

 and indeed very distinct in all their characters ; although, as will 

 hereafter be more particularly noticed, in all probability of cori- 

 teniporaneous origin." 



" The granite, generally speaking, is large-grained, and very 

 frequently possesses that particular arrangement of the crystals 

 of felspar that entitles it to the epithet porphyritic. This cha- 

 racter may indeed be said to be almost universal, and is exem- 

 plified in the pillars of almost every field gate Almost the 



only foreign ingredient (with the exception of the metaUic ores 

 in the neighbourhood of some veins and floors of tinstone), con- 



