SCHISTS OF THE LIZAED DISTEICT. 7 



latter seem to form a kind of littoral fringe to the great mass of ser- 

 pentine inland. Some of the former show very interesting inter- 

 banding of the granitoid and dark varieties, layers from less than 

 half an inch to an inch setting in and dying out — indicating almost 

 certainly lenticular bedding (PI. I. fig. 1). This is seen on a larger 

 scale in the granitoid rock at the north end of the cove described 

 in my last paper (p. 901)*. 



We seem then to have satisfactory evidence from these sections 

 along the eastern coast that the rather uniform and thick mass of 

 hornblende schist passes upwards into a more variable group, charac- 

 terized by the presence of quartzo-f elspathic bands, which can hardly 

 be less than two or three hundred feet thick, and may be more. 



The coast for some miles northward is occupied by serpentine and 

 gabbro, and a great part has been minutely described in my former 

 paper ; but as hornblende schist is not marked on the map, and 

 as I had no recollection of seeing any, I did not think it necessary 

 on the present occasion to examine this, but commenced again at 

 Porthoustock Cove, to the north of the great mass of " greenstone " 

 forming Manacle Point, at which my former work ended. The cliffs 

 on the southern side of the cove consist of " greenstone "f. On the 



* At the base of the rocky projection which divides Kennack Cove into two 

 bays a singular rock occurs, as to the nature of which I feel much difficulty in 

 coming to a conclusion. It consists mainly of a finely crystalline mixture of 

 felspar, hornblende, and brown mica, with a slight indication of parallelism in 

 its mineral structure ; but here and there it seems to become porphyritic or is 

 spotted with patches of a felspathic mineral and a dull green, rather fibrous, 

 hornblende like some of the altered gabbros on this coast ; many of these seeming 

 enclosures vary up to about 3" across, but sometimes they are as much as a foot 

 or two wide. The appearance suggests that we have here a mass of igneous 

 rock which has broken through and brought up with it a number of fragments 

 of gabbro. The mass includes bands resembling the granitoid rock of the neigh- 

 bourhood, and appears to end rather abruptly. Felspar veins traverse it and 

 add to the confusion. Microscopically it consists of a rather pale green horn- 

 blende, felspar mostly replaced by microlithic secondary products, some rather 

 altered brown mica, together with some apatite, black iron-peroxide, and a little 

 quartz. Here and there are aggregated grains of rounded outline and minute 

 granular structure, which, with crossed Nicols, give a minute speckling of different 

 rather bright colours. This mineral is often associated with grains of magnetite _ 

 (?) and sometimes seems to enclose them. The hornblende resembles that already 

 described from a dyke in Kennack Cove (vol. xxxiii. p. 901), and has the look 

 of a " uralitic" mineral. The felspar, however, seems to have been in rather 

 rounded grains, not in the elongated prisms common in dolerite; we meet, 

 however, with the former shape in gabbros and some diorites, so that I incline, 

 though not without hesitation, to regard this as an igneous rock. 



t Two specimens of this have been microscopically examined. Both exhibit 

 rather elongated crystals of a plagioclastic felspar, considerably decomposed, 

 extinguishing at angles which are most in agreement with those of labradorite, 

 together with hornblende, which, from its irregular external form, its feeble 

 dichroism and absence of characteristic cleavage, I believe to be a secondary 

 product. There are specks and rods of opacite with a little ilmenite (probably) 

 and pyrite. The rock was probably once a dolerite, and so may be named a 

 hornblendic diabase. 



The above is cut by a dyke of felspathic gabbro. This sends off veins into the 

 adjacent rock, and its greatest thickness is about 4'. It consists of a rather 

 decomposed plagioclastic felspar, with the " granular " outlines usual in gabbro, 

 agreeing best with labradorite, and of a green mineral, which often occurs as 



