166 A. Somervail — Schists of the Lizard District. 



seems good reason for supposing that the one -magma may have 

 contained within itself the elements of the whole, which became 

 ultimately more or less differentiated. 



In many instances, as at West Kennack Cove, the highly interest- 

 ing and instructive Kildown Cove, and other localities, there are 

 rocks quite intermediate in character and composition between the 

 granitic and dioritic types. These rocks are in close juxtaposition 

 to both granite and diorite, and decidedly form a portion of them, 

 the whole rising together through the adjoining serpentine. These 

 intermediate rocks frequently form great homogeneous masses with- 

 out any intermingling of other varieties, or without any banded 

 structure whatever. They are only semi-granitic or granular in 

 texture, and in composition contain hornblende, quartz, felspar, and 

 perhaps a little mica; yet they are neither granites nor diorites 

 proper : still, from this stage, we can trace them into both, also into 

 varieties with a well-defined banded structure, in which sometimes 

 the granitic and sometimes the dioritic constituents predominate. 



Such intermediate varieties of rock are frequently found both on 

 the coast and in inland directions rising through the serpentine. 

 A dyke of this description, cutting through the serpentine, occurs 

 at Trelease Moor, from which might be collected several distinct 

 varieties of rock, ranging between the granitic and dioritic types. 

 On the coast, as immediately east of the Yellow Carn and at many 

 other localities, there are groups of dykes close together penetrating 

 the serpentine, which I believe to be all related, which likewise 

 vary from the dark compact dioritic type to the " granulitic " or 

 granitic variety. 



At Kildown Cove, near the centre of the " granulitic " mass 

 which there appears to me to cut the serpentine, is a rudely circular 

 and concretionary-like nodule, made up of concentric layers of 

 alternating " granulitic " and dioritic rock, with a central nucleus 

 of granitic material, in which are also patches of hornblende. The 

 teaching of this singular and instructive complex nodular mass 

 appears to me not only to have a very decided and direct bearing, 

 not only on the origin and relations of these " granulitic " and 

 " hornblendic " rocks, but also on the origin of these banded 

 structures. 



The important question now arises, are these " granulitic " or 

 granitic and dioritic dykes portions of the great masses representing 

 these two groups? My own observations incline me to reply that 

 they are, for the following reasons : — 



1st. The similarity, if not the exact identity, between the rocks 

 composing the dykes and those forming the two groups proper. 



2nd. The apparent connexion between the dykes and large masses 

 of admitted granulitic and hornblendic rocks which seem to be their 

 feeders. 



3rd. The entire absence of these, or similar true eruptive ' dykes, 

 cutting the massive portions of either of the two groups, 2 which we 



1 The dykes in the outer rocks off the Lizard Head seem to me to be segregation 

 dykes. 2 Attention to this has been drawn by Mr. Teall. 



