16 PROF. T. G. BONNEY ON THE HORNBLENDIC AND OTHER 



a different aspect from the smaller ones, which contain numerous 

 microlithic enclosures of opacite and of a nearly colourless mineral. 



(3) Specimens of massive hornblende schist from near the fault 

 in Polurrian Cove (p. 10). Minerals similar to those in No. 1, but 

 the structure of the rock is a little coarser and more granitoid. 



(4) Finely banded epidotic rock, Cadgwith Cove (p. 6). Horn- 

 blende, felspar (very decomposed), much epidote, and some quartz ; 

 separation of the minerals into layers very marked ; sometimes 

 epidote predominating. Microliths frequent, similar to those de- 

 scribed above, fairly characteristic sphene, and a grain or two of 

 pyrite. Cracks roughly transverse to bedding-planes, filled with a 

 minute granular brownish mineral, like one which here and there 

 replaces the felspar. 



(5) White-banded hornblende schist, in Carnbarrow crags near sea 

 to north of Dolor Hugo (p. 6). Structure similar to last, but 

 little or no epidote, rock being chiefly hornblende and felspar. 



(6) White-banded hornblende schist, almost touching serpentine 

 on west side of mass, Porthalla Cove (p. 9). The felspar in this 

 specimen is almost wholly replaced by granular brownish earthy 

 minerals. The hornblende nearly colourless, similar in appearance 

 to the " uralite " occuring in gabbros ; a crack is filled with arago- 

 nite. The minerals in this rock have obviously been altered con- 

 siderably since the period when they first crystallized ; but there is 

 no appearance whatever of a " passage " into the serpentine. 



(7) Hornblende schist from crag just south of the termination 

 of the serpentine, at the south end of Pentreath Beach. The minerals 

 are in a condition very similar to those described in the last case, 

 but the rock is a little coarser and more schistose in structure. 



C. Granulitic Group. 



Two very common types of rock in this series, often inter- 

 banded, and so producing the most conspicuously stratified por- 

 tions, are the following: — one a rather finely granular pinkish- 

 grey rock, composed mainly of quartz and felspar, with occa- 

 sional specks of a dark mineral forming inconspicuous bands ; 

 the other a dark grey rock, in which the last-named mineral 

 clearly predominates. Neither is conspicuously fissile, the former 

 the less so. It exhibits almost every gradation, from a rock 

 closely resembling a vein-granite to a rather felspathic quart- 

 zite. I have selected as types of the ordinary bands two speci- 

 mens collected from the north side of the Frying Pan, Cadgwith 

 (p. 6). Under the microscope, the first consists chiefly of grains 

 of quartz and felspar, both being irregular in outline and variable 

 in size, together with a dark mica and a little hornblende. 

 The quartz contains in places minute filmy microliths and cavities, 

 the latter varying considerably in size ; but they cannot, as a rule, 

 be examined unless magnified from 200 to 300 times at least. Bub- 

 bles are sometimes, but by no means universally, present. These 

 certainly do not always occupy the same amount of the cavity : some- 



