Yol. 52.] ROCKS OE THE LIZARD DISTRICT. 33 



schist, and seems to pass rapidly into the adjoining serpentine. 1 In 

 the field I came to the conclusion that the latter rock had intruded 

 into the former, occasionally breaking off pieces of it and even locally 

 melting them, wholly or in part. Let us then see how far this con- 

 clusion is supported by study with the microscope. Taking first a 

 slice cut from a specimen which showed (as I supposed) a junction of 

 the serpentine and hornblende-schist, I find that the greater part 

 consists of a serpentine (mineral) of a brownish or greenish- orange 

 colour, exhibiting a structure which, if this were an acid rock, I 

 should not hesitate to claim as fluxional. In this groundmass are 

 scattered clear grains of a mineral without definite external form or 

 any well-marked cleavage, which, however, I think may be identified 

 as a hornblende, together with one crystal of a serpentinized bastite, 

 including rods of a monoclinic pyroxene. Besides these are numerous 

 granules, often aggregated, of a fairly translucent brown mineral ; 

 some, doubtless, are picotite, but others, which exhibit double refrac- 

 tion, are probably haematite. This part is succeeded by a streak rich 

 in pyroxenic grains, many of them light brown in colour ; and the 

 latter rock (sometimes after an intervening film of the former one) 

 changes to a band (slightly irregular in outline) consisting of felspar, 

 in a very decomposed condition, 2 of hornblende, warm brown in colour, 

 and of a moderate number of grains, which probably are a white augite, 

 though the mineral is rather ' dirty ' and sometimes serpentinized. 

 This band is about i inch wide, and the slice then is ended by a 

 serpentine like that already described. But on examining the hand- 

 specimen, this serpentine appears to be little more than a film, for 

 in not more than one-fifth of an inch we find fairly normal horn- 

 blende-schist. Next let us take two specimens from a part of my 

 friends' section 3 near the porphyritic dyke. It is thus described in 

 my notes : — ' A curiously banded and streaked rock, exhibiting fine 

 compact bands and coarser-looking brown bands, in parts much 

 wrinkled and once or twice slightly brecciated, somewhat resembling 

 serpentine, but rather harder than is usual with that rock. I have a 

 strong suspicion that this is a mixture of serpentine and horn- 

 blende-schist, the latter being partly melted down by and carried 

 along with the former.' Of one specimen, cut where the streaky 

 structure is much curved, one would claim part, without hesitation, 

 for hornblende-schist. It exhibits (PI. I. fig. 5) the usual rather 

 granular structure, and consists mainly of a felspar, somewhat de- 

 composed, and hornblende, which, however, is brown instead of the 

 ordinary strong green colour. In other parts (streaks) we find the 

 grains of brown hornblende in a ' matrix ' of composite microgranular 



1 I suppose, of course, that the serpentine was a peridotite at the time of 

 the intrusion. This must be understood throughout. 



2 It is whitish by reflected light, earthy brown by transmitted, and shows 

 specks of brightest colour with crossed nicols. 



3 Op. cit. p. 203 (map). I think it is from the part 8 and Sch below the 

 patch marked e. Whether this be the top of a ' dome ' or not, I believe it to 

 be an included mass, or, at any rate, to indicate intrusion on the part of the 

 serpentine. 



Q. J. G. S. No. 205. d 



