Tol. 52.] BOCKS OF THE LIZARD DISTRICT. 23 



softened, drawn out, and even locally melted down and absorbed 

 by the former. One section, which I found on the southern side 

 •of Kennack Cove, so well illustrates this process that it deserves, 

 perhaps, a brief description. A light-greyish granite is intrusive into 

 .a dark dioritic rock, which it has shattered into a breccia, but in 

 places one can see that the latter is locally melted by and incorporated 

 with the former, the result being a regular, rather fine-grained, 

 streaked or banded gneiss. 1 I obtained specimens of all three rocks 

 and have examined them under the microscope. The granite consists 

 mainly of quartz and felspar, with a rather small amount of biotite 

 .(somewhat bleached). 2 The structure is granular, only one or two 

 of the larger felspars showing any approach to a crystal-outline, 

 and the grains differ much in size. It exhibits the association of 

 this mineral and the quartz to which I have often called attention 

 .as more characteristic of a gneiss than a normal granite, 3 with a 

 •very slight approach to a linear order in the constituents. The 

 ■dioritic rock consists of felspar, rather decomposed, apparently 

 plagioclastic, green hornblende, biotite (not much, and rather 

 sporadic), with a little sphene, etc. The structure is granular, 

 with occasionally an approach to ophitic, and felspars, 4 or 5 times 

 -the diameter of the rest, occur sparsely. The banded gneiss has a 

 general resemblance in structure to the granite, except that its 

 felspars are even more variable in form and size, the linear ordering 

 .of the constituents is more marked, and grains with micropegmatitic 

 structure, which are rare in the other rock, are common here ; 

 apatite is more conspicuous and two or three very small garnets 

 occur ; there is a considerable amount of a rich brown biotite, but 

 jhornblende is absent ; at least I do not find a single scrap (there 

 are a few green flakes) that I can identify with certainty. On the 

 •significance of this I have already written. 4 



Additional evidence, however, was obtained in regard to one 

 point of interest. I have always believed the granulitic group to 

 overlie the hornblendic, though I felt that the evidence in favour of 

 this was not very strong. The latter rock usually occurs in great 

 continuous masses, the former in more or less interrupted blocks, 

 which, though they may be sometimes traced with but little inter- 

 ruption for considerable distances, are associated (always so far as I 

 remember) with the serpentine, and occur in such a manner as to 

 give the impression that they are fragments of a mass which it has 

 shattered, and in some cases actually transported. In one place, 

 however, in the crags on the south side of Cadgwith Cove, as men- 

 tioned in our former paper, 5 the granulitic rock appeared to be 

 superposed on the hornblendic schist. On the last occasion, favoured 



1 The specific gravity of the granitic rock is 2-611, of the dioritic 2-917, of 

 -the banded gneiss 2 - 628 : intermediate, but, as we might expect from its appear- 

 ance, nearer to the first. 



2 In these descriptions and throughout the paper, minor details of composition 

 .and structure are suppressed, as being without significance for my main purpose. 



3 Quart. Journ. G-eol. Soc. vol. xxxvi. (1880) p. 97, etc. 

 * Bid. vol. xlviii. (1892) p. 132. 



5 Ibid. vol. xlvii. (1891) p. 478. 



