508 A. Somervail — Banded Rods of the Lizard District. 



more or less pure, or mixed with quartz, more or less granitic ; the 

 paler shades consisting of the former, the darker of the latter. 



Trelease Moor. — The rocks here, which I referred to in my last 

 paper as rising through the serpentine, and as formed of several 

 distinct varieties of rock, ranging between the dioritic and granitic 

 types, I have found in a recent visit, also, to be most distinctly 

 banded, the granulitic bands passing gradually into the more basic 

 portion of the rock. 



Although the banded structure exists in the granulitic rocks on the 

 south coast, near the Lizard Head, and in the outlying reefs, and 

 at the Yellow Carn, also on the west coast at George's Cove, yet it 

 presents no special features beyond what has already been noted in 

 the foregoing localities. 



In the " hornblende " group the banding is of a much less complex 

 character, the bands of whatever minerals they may be composed 

 having as a rule a linear arrangement. They generally consist of 

 alternations of felspar and hornblende, the latter more pure and 

 granular or crystalline than the base of the rock, the former also 

 differing much in its exemption from other minerals, and likewise in 

 its colours. The felspar bands are not always uniform and parallel, 

 but frequently occur in lenticular patches, and display other irre- 

 gularities. In thickness they vary from the thinness of a sheet of 

 paper up to bands of a couple of feet or more as at George's Cove. 

 There are also numerous bands of epidote, but they are only to be 

 regarded as an alteration product of the hornblende. Besides the 

 parallel banding in the hornblende group there is another type of 

 less regular banding, gradually becoming more so until the arrange- 

 ment of the bands are lenticular and the rock in appearance like 

 a well-foliated gneiss. 



These gneissose rocks can be studied at the base of the old Lizard 

 Head, and the outlying rocks; also, in those of the Dranna rocks 

 which lie immediately off Porthkerris Point, east of Porthallow. 1 

 Others of a similar nature have been described by Mr. Howard Fox, 

 on the fore-shore south of Ogo Dour Cove. 2 



II. Origin of the Banded Structure. 



It is a remarkable fact that all the great distinctive varieties of 

 rock in the Lizard district exhibit more or less of a banded structure. 

 As is well known, it is present in the gabbro, and even the serpen- 

 tine is not free from it. 3 A good example of very distinct banding 

 may be seen in the green serpentine of Kildown Cove, and I have 

 noted a similar banding in other localities, over and above the 

 distinct thin layers, or bands of nearly pure hornblende which 

 traverse, even, the true serpentine as at Gue Graze. 



1 The gneissic rocks from both of these areas were shown me by Mr. Howard Fox, 

 F.G.S. In the latter locality I would not have suspected them to occur. 



2 Junction of the Hornblende Schist, etc., Trans. Boy. Geol. Soc. of Cornwall, 

 1889, vol. xi. part iv. p. 213. 



3 Vide paper by Mr. Kutley, Trans. Eoy. Geol. Soc. Corn. vol. ix. part 4, 1889, 

 pp. 239-241. . 



