44 



PR0E. T. G. BONNET ON THE SERPENTINE 



Pig. 3. — Quarry at Plas Goch. 



A. Green schist, well marked dip. 



B. " Steatite " schist, partially quarried out. 



0. Green schist, most massive and serpentinous-looking at X . 



It is very soft, like talc, and greasy to the touch, of a pale dull green 

 or leaden colour. C is a less pure steatitie schist, which at D 

 assumes a more normal character, and it dips to N.N.W. or 1ST. x is 

 more like a serpentine, and has more the aspect of an intrusive rock ; 

 it is of a dull-green colour, and has a slightly schisty structure, is 

 harder than E, but can just be scratched with the nail. It contains 

 numerous crystals of magnetite, commonly minute, but in places very 

 distinct octahedra, which are sometimes nearly J inch in diameter. 

 The matrix, however, on close examination, rather resembles a 

 massive chloritic rock, like some of the lapis ollaris of the Italian 

 Alps (e. g. that from near Chiesa in the Yal Malenco) than a true 

 serpentine. To the latter, under the microscope, it has little 

 resemblance. It consists of a thickly felted mass of a scaly or 

 fibrous clear mineral, slightly tinged with green, and feebly dickroic. 

 The brightest tint shown with crossed Mcols is a dull greyish white ; 

 and the mineral is either hexagonal or orthorhombic ; minute gra- 

 nules; some fairly clear, some brown to opaque, are scattered about 

 the slide (the larger crystals have been apparently torn out in pre- 

 paring it), part of which are probably chromite. After two visits 

 to the pit, and the best study that I can give to the rock, I am dis- 

 posed to think that it is more probably a massive chloritic schist 

 than a true serpentine, and that the appearance of intrusion is 

 illusory. The quarried rock (B) under the microscope exhibits a 

 thickly felted mass of almost colourless folia, which, in transverse 

 section, do not show conspicuous foliation, together with some few 

 scattered granules of opacite. With crossing Nicols they afford fairly 

 bright pink and green colours, and are almost certainly talc, so that 

 the rock may be regarded as a talc-schist.* 



The following are the results of the microscopic examination of 

 some of the above-mentioned rocks. The porphyritic rock found near 



* I am since indebted to F. T. S. Houghton, Esq., F.G.S., for the following 



