SCHISTS OF THE LIZAKD DISTRICT. 23 



myself with remarking that Dr. Sterry Hunt has never seen the 

 Lizard district. 



The serpentines of the Lizard district afford us some varietal dif- 

 ferences which, hereafter, on a more minute study than can be 

 given by one who is only a visitor to the country, may possibly 

 prove to be of importance. The handsome mottled varieties, with 

 conspicuous crystals of bronzite, occur chiefly in the southern and 

 south-eastern regions, along the coast from the Balk, near Lande- 

 wednack, to Coverack Cove, and for a considerable distance inland, 

 at any rate to the neighbourhood of Ruan Major, the tine black 

 variety with glittering bronzite crystals being found on the coast south 

 of Caerleon Cove ; they occur also on the western coast some dis- 

 tance to the north of Kynance Cove (near the " Horse "), South of 

 that, in the cove itself, and at the Rill, as well as to the north at 

 Gue Graze, George Cove, and near Mullion Cove, compact dull- 

 coloured varieties are commoner, and these are seen by the Helston 

 road on the northern part of the mass. In close association with 

 these is the dull-coloured variety, containing small glittering crys- 

 tals, which appear to be mainly a pyroxenic or hornblendic mineral *, 

 found especially about Lower Pradanack and in Mullion Cove, but 

 occurring locally also in one or two localities on the eastern coast 

 about Dolor Hugo and the Prying Pan. A streaky structure is not 

 seldom visible in these dull-coloured varieties, and this is especially 

 conspicuous in the outlying mass at Porthalla, and in the more 

 eastern part of the northern edge of the great mass on' Goonhilly 

 Downs (though here the rock is more highly coloured). I am 

 distinctly of opinion, after reviewing all my specimens, that several 

 of them, and notably the thin dykes at the foot of the crags north 

 of Kynance Cove (vol. xxxiii. p. 920), have formerly been in a 

 glassy or semicrystalline condition f. 



The result of the above examination of the " Hornblende schist" 

 shows that it can no longer be regarded as a metamorphic repre- 

 sentative of Lower Devonian (or even Silurian) strata, but that it 

 almost certainly belongs to some part of the Archaean series. As, 

 then, the lower limit of the time during which the intrusion of the 

 serpentine may have taken place is extended so enormously back- 

 wards, it seems at present hopeless to attempt to conjecture (as I 

 did in my last paper) at what geological epoch this event may have 

 happened, the only clue furnished us being that the serpentine on 

 the western coast is cut by granite veins which are probably of the 

 same age as the great masses further north, that is, later than a 

 good part of the Carboniferous and earlier than the Trias. 



* In my former paper I called it augite, as it was practically colourless, and 

 exhibited no dichroism. As it happened, none of the slides gave specimens with 

 characteristic hornblende-cleavage. But I find the extinction-angles agree better 

 with hornblende, and a specimen subsequently collected from near Lower Pra- 

 danack gives several transverse sections with indubitable hornblende-cleavage. 



t See Prof. Renard, " Peridotit von der St. Paul's Insel im Atlantischen 

 Ocean," Neues Jahrbuch, 1879. Also "Report on Petrology of St. Paul's," 

 ' Challenger ' Voyage (Narrative), vol. ii. 



