A. Somervail — Schists of the Lizard District. 167 



might reasonably have expected to find, had the dykes been a 

 separate and later product. 



When we come to examine these " granulitic " and "hornblendic" 

 rocks in their massive conditions and relations, and not confined to 

 mere dykes or small exposures, then we have more light thrown 

 upon them. We find them both in isolated and associated masses 

 of great extent, and if we were able to trace them fully out in a 

 seaward direction, they would seem to completely encircle the 

 entire area of the serpentine and gabbro. 



The " granulitic " portion can now no longer be regarded as con- 

 fined to the east coast, as stated by Prof. Bonney, but is more or 

 less extensive with nearly every portion of the entire coast-line. It 

 forms the rocks all round the base of the Lizard Head. 1 It occurs 

 at North Caerthillian, Holestrow, in great force at and near George's 

 Cove, and also sparingly so at other localities. 



The great extent of the dark hornblende schists exposed on the 

 south coast is clearly connected with the " granulitic " at either 

 extremity, and also to a small extent on the south where the schists 

 approach the serpentine. We find a connection between the dark 

 hornblende-schists and the typical " granulitic " on the east at a 

 little cove south of the Lower Balk Serpentine Quarry, where we 

 are able to trace the transition between both. On the west we are 

 able to trace the same relations at Caerthillian, and at George's 

 Cove the dark hornblende-schists or rocks are distinctly traceable by 

 a gradual transition into the typical " granulitic," which occurs there 

 in considerable force. On the east coast, as at Carnbarrow and 

 Cadgwith, the typical hornblende- schists may be seen passing into 

 the " granulitic " rocks, an excellent example being the fine section 

 on the portion of the cliff between the Frying-pan and Cadgwith, 

 which here clearly shows the very gradual transition of the one 

 group into the other. 



Altogether I think that the gist of the whole evidence is clearly 

 to prove that both groups have had a common origin, and that the 

 granulitic or granitic portion is not intrusive in the dioritic, or vice 

 versa, but that both are part and parcel of the same magma. Sub- 

 sequently these rocks may, and indeed have been deformed, and 

 crushed up together, as at the Lizard Head, and other localities, but 

 even here, with all the intricate confusion and alterations in their 

 mineral aspects arising from this crushing and deforming process, 

 the relations existing between these rocks show I think no indica- 

 tions of intrusion. 



General McMahon 2 in his paper has certainly called attention to 

 one instance of intrusion into the granulitic. He says, p. 533, 

 " One of the intrusive diorites is well seen at Polbarrow, where 

 a broad dyke of it cuts right across the 'granulitic' group between 

 the ruined boat-house and the cliff. Down below veins of it may 

 seen intruding into the granulitic." 



1 These rocks appear to me to have a decided claim to be ranked as portions of the 

 " granulitic " group. 



2 Quart. Journ. Geol. Soc. vol. xlv. 



