composition of the mother-rock, may be recognised in the Lizard district. 

 These varieties can, however, in many cases only be distinguished from each 

 other by the examination of thin slices under the microscope. Some of the 

 serpentines appear to have been derived from an olivine rock (dunite), others 

 from an olivine-enstatite rock (saxoiiite) and others from an olivine-enstatite- 

 augite rock (Iherzolite). In the oliviiie-eustatite serpentines the latter 

 mineral is more frequently represented by porphyritic crystals of bastite 

 which yield bright glistening cleavage surfaces. The black serpentine so 

 largely developed on the coast at various points to the north of Cadgwith, is 

 a good illustration of this variety. Near Mullion Cove, Ky nance Cove and at 

 some other localities, rocks largely composed of olivine and hornblende occur, 

 and in some of these the latter mineral is quite as abundant, if not more 

 abundant than the former. Both minerals pass over into serpentine. 

 Another point of considerable interest in relation to these rocks is the fact 

 that they frequently show a marked banding due to a variation in the relative 

 proportions of the different constituents. In this respect, as also in respect of 

 their original mineralogical composition, they bear a close relation to the 

 peridotites of the Almeklovdal type described by Messrs. REUSCH & BROGGER. 

 The latter rocks, are, however, perfectly fresh, whereas the Lizard rocks are 

 all more or less serpentinised. Porphyritic crystals of bastite may occasionally 

 be observed in the olivine-hornblende serpentines, but as a rule they are absent. 

 The occurrence of bastite is of importance, because it serves to link the 

 serpentines containing hornblende with those from which this mineral is 

 absent. Picotite also occurs in the olivine-hornblende serpentines. 



Speaking of the distribution of the different varieties Professor BOXXEV 

 says: "The handsome mottled varieties, with conspicuous crystals of bronzite 

 [bastite] occur chiefly in the southern and south-eastern regions, along the 

 coast from the Balk, near Landewednack, to Coverack Cove, and for a 

 considerable distance inland, at any rate to the neighbourhood of Huan Major, 

 the fine black variety with glittering bronzite [bastite] crystals being found 

 on the coast south of Caerleon Cove ; they occur also on the western coast, 

 some distance to the north of Kynaiice Cove (near the Horse). South of 

 that, and at the Rill, as well as to the north at Guc 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 

 crystals, which appear to be mainly a pyroxenic or hornblendic mineral 

 [grammatite], found especially about Lower Pradaiiack and in Mullion Cove, 

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

 Dolor Hugo and the Frying Pan. A streaky structure is not seldom visible 

 in these dull coloured varieties, and this is especially conspicuous in the out- 

 lying mass at Porthalla, and in the more eastern part of the northern edge of 

 the great mass on Goouhilly Downs (though here the rock is more highly 

 coloured)." 



