A. Somervail — Schists of the Lizard District. 163 



mapped by him, are in beds of considerable thickness, and occur on 

 several horizons in the hornblende-schists. 



There is also the felsitic-like-rock at Housel Cove, 1 described by 

 myself as an altered hornblende-schist, but which, I meant to have 

 added, might have been the original rock in a more or less altered 

 form, out of which the hornblende-schist had been made. 



Still further, among the dark hornblendes of Pradnack we find 

 quartzose and quartzo-felspathic varieties, and even a rock approach- 

 ing the granulitic type south of the serpentine junction near Rynian. 

 There are also small bands of felspar and quartzo-felspathic matter in 

 the hornblende-schist at the landing-place in Landewednack Church 

 Cove, which, however limited in extent and thickness, have yet their 

 own bearing. 



All these rocks are more or less connected by a passage into 

 each other, and the whole in turn pass into the rocks of the 

 "granulitic" group, from which they cannot be separated. 



III. Talco-Micaceotjs Group. 



This group of rocks was originally described by Mr. Majendie, 2 

 Dr. Boase 3 and De la Beche, 4 and is principally confined to the 

 extreme south-west coast between Polpeor Cove and Caerthillian ; 

 a line between these two localities drawn inland being represented 

 on the Survey Map as the boundary separating this group from the 

 hornblendic. 



With the addition of the outlying rocks described by Messrs. 

 Teall and Fox, 5 which are certainly connected with those of the 

 mainland, this group seems to me to be nothing more than the 

 mere altered states of the two former groups, the " granulitic " and 

 " hornblendic." The rocks which compose it, in their less altered 

 conditions are essentially on the one side those of the quartzo- 

 felspathic or " granulitic " type, and on the other, those of the 

 " hornblendic." It is quite true that there are rocks differing 

 widely from both, such as the mica-schists, mica-diorites, actinolitic- 

 schists, chlorite-schists, etc.; but if these can be shown to be but an 

 altered form of the " hornblende " group — as I think it can — it will 

 simplify very much the geology of this complicated area. 



Again, all the above-mentioned rocks', along with intermingled 

 masses of less altered hornblende, are seen to shade into each other 

 in the most perfect manner, almost in every locality in this area 

 a passage being noted from one to another. There is sometimes a 

 transition from the compact hornblende to the greenish schist, as 

 seen near, or between Pentreath Beach and Caerthillian, other 

 examples extending as far as Polpeor Cove ; passages from the 

 hornblende into chlorite-schist as at the Crane, from the former 

 rock into actinolitic-schist at the Lizard Head, and into mica-dioritic, 

 and this into mica-schist, at the same and many other localities. 



1 Geol. Mag. Decade III. Vol. VI. p. 114 (1889). 



2 Trans. Geol. Soc. of Cornwall, vol. i. p. 31 (1818). 



3 'I rans. Geol. Soc. of Cornwall, vol. iv. p. 341 (1S32). 



4 Report Com. Devon, etc. p. 29 (1839). 



5 Quart. Journ. Geol. Soc. vol. xliv. p. 309. 



