ASSOCIATED ROCKS OF THE LIZARD DISTRICT. 901 



the lower part of which bifurcates; and just beyond this is an in- 

 cluded fragment of schist of singular form. The dyke in the mass 

 has a slightly serpentinous aspect. It is a finely granular, almost 

 .compact, very dark grey rock, faintly variegated with minute white 

 specks. Under the microscope its appearance is as follows : — There 

 is a tolerably clear homogeneous-looking base containing a large 

 number of small prismatic crystals and folia of greenish hornblende 

 with fairly marked dichroism, and a good many small grains of 

 magnetite. With the two Nicols the base exhibits the microcrystalline 

 pseudomorph after felspar, and the hornblende shows brilliant colours. 

 A little has a rather fibrous structure, and on rotating the stage be- 

 haves as an orthorhombic mineral ; it is strongly dichroic, showing 

 a brown tint (? anthophyllite) ; there is, however, not enough to 

 enable one to be certain about it. A vein is filled by asbestiform 

 mineral, possibly a variety of chrysotile. 



Proceeding along the shore we pass in quick succession some 

 other narrow dykes (three, I think) of very similar appearance. 

 The last but one (2 to 3 feet thick) cuts through a vein of coarse 

 gabbro about 10 inches thick, which shows again in one or two places 

 in the face of the cliff. A little to the north it is apparently cut by 

 another dyke; but after carefully examining the latter, especially 

 where it is exposed on the shore, I believe it to be only an in- 

 cluded fragment of a peculiar compact variety of the schist, highly 

 altered. About 30 yards to the north is another included mass of 

 the schist, standing upright in the serpentine cliff so as to look won- 

 derfully like a dyke. 



Just where the sandy beach of Kennack Cove commences is 

 another large mass of included schist, occasionally resembling vein 

 granite, which may be traced some way inland. Two or three in- 

 trusive tongues of highly decomposed serpentine may be seen in 

 this mass. 



Kennack Cove is a sandy tract at the embouchure of two flattish 

 valleys, divided by a low headland of serpentine. In this is a small 

 dyke about a foot (or rather less) thick, closely resembling those 

 described above, but perhaps even more compact. 



Crossing the second stretch of sand we come again to cliffs of 

 dark serpentine, and find almost at the first point a dyke, generally 

 from 4 to 5 feet thick, which bifurcates above. The appearance of this 

 rock is very similar to those already described. Under the micro- 

 scope it is found to consist of longish, rather irregularly outlined, 

 plagioelase crystals, and a quantity of aggregated grains or imper- 

 fectly shaped small crystals of hornblende, green-coloured, strongly 

 dichroic, and showing bright colours with polarized light. There 

 are also some irregular grains of magnetite and a few needles of 

 apatite. 



A short distance further along the shore a mass of rock, forming a 

 group of low reefs, bears, at first sight, a close resemblance to a 

 granite vein. This is heightened by the extraordinary way in which, 

 in one place, it inserts itself in thin tongues into the adjoining 

 rock, which is a crumbling, dull, greenish to reddish substance, not 



Q. J. G. S. No. 132. 3n 



