SCHISTS OF THE LIZARD DISTRICT. 9 



hillside, near to which a junction is seen with banded hornblende 

 schist (generally similar to that just mentioned), and down on the 

 rocky shore at low water, where this rock and its junction with the 

 hornblendic series may be studied to great advantage, and some 

 interesting facts observed which will be noticed below. Altogether 

 there is a considerable mass of serpentine, beyond which a distinctly 

 banded whitish and dark greenish hornblende schist can be traced up 

 from the sea, forming the whole mass of this part of the hill. The 

 dip at first varies towards either side of north, with much distur- 

 bance and rolling ; then it becomes N.W., and, finally, at about 

 one third of a mile from Porthalla, it is almost N.N.W., the angle 

 being nearly. 50°. 



The slaty rock, which extends from Porthalla Cove northwards, 

 has been excellently described by Sir H. De la Beche ; and I only 

 made a rapid traverse as soon as I had satisfied myself that it had 

 no claim to be called a foliated rock, and exhibited no marked 

 metamorphism, unless a probable slaty cleavage (coincident with 

 bedding) be so called. Hence I content myself with referring to 

 the microscopic structure of the generally similar series on the 

 western coast (p. 11), and, passing over the quartzose and calcareous 

 bands, at which I have merely glanced, proceed on to a locality 

 to which, as having an important bearing on the relation to the 

 hornblende-schist series, 1 paid particular attention. Sir H. De la 

 Beche draws attention to three conglomerates which he observed 

 in this slaty series. The most distant of these I had not time to 

 visit ; but I made a brief examination of that west of the Nare 

 Point and a much longer one of that to the south of it. The former 

 is peculiar. I did not notice the rounded quartz pebbles mentioned 

 by Sir H. De la Beche, and the majority of the blocks are but 

 little rounded; some have a vesicular aspect and resemble a dark 

 greenstone. I thought this might possibly be an agglomerate ; but 

 a specimen examined microscopically proves to be a dark quartz 

 grit, such as might have come from one of the older Palaeozoic 

 rocks. As to the character of the bed south of the Nare Point, there 

 can be no doubt it is a true conglomerate, containing in a dull-grey 

 muddy-looking matrix angular fragments of dark slaty rock, of a 

 kind of dark " greywacke," of vein-quartz, and a quartzo-felspathic 

 rock bearing some resemblance to the pseudogranitic bands already 

 mentioned* ; the last two are pretty well rounded, as if they had 

 travelled further than the other. The materials of the conglomerate 

 vary much in size; sometimes they are qnite small, sometimes 

 (especially in the upper part) up to, and even exceeding, a foot in 



• * Microscopic examination shows it to be a true gneiss, though not one of 

 the most conspicuously foliated varieties. It consists of quartz, often in aggre- 

 gated patches of grains of different sizes, felspar (orthoclase, with some albite 

 or oligoclase, and possibly a little microcline), a fair quantity of colourless 

 mica (probably one of the hydrous potash or soda group), and a less amount of 

 a much altered magnesia-iron mica. 



This specimen has more white mica than is usual in the granulitic group, 

 and may have come from some other series, such as that to which belong the 

 gneisses near the Eddystone, 



