126 



the Survey Memoir on the district/ 1 ' but they have received more extended 

 notice by Professor BOXXEY (2) from whose paper the following account is 

 taken. The ordinary rock of the district in which the serpentine occurs is 

 " a dull bluish or greenish schist, composed chiefly of minutely crystallised 

 micaceous or chloritic minerals with some quartz." This rock often exhibits 

 the most remarkable crumplings. Gabbro is also found in intimate relation with 

 the serpentine, and the colour representing the latter rock, on the map, is often 

 made to include the former. The gabbro is often foliated as at the Lizard, and 

 on the bank of an inlet near Tyddyii Gob, " is a rather schistose rock which 

 in the lower part resembles a foliated gabbro, in the upper a schist." At 

 Ty Ucha the serpentine shows the characteristic net-like structure and 

 " probably results from the alteration of an olivine-rock a kind of dunite." 

 Near Cruglas Farm serpentine veined with calcite occurs, and in some 

 places the rock is a kind of ophicalcite. At Ceryg Moelion a crushed 

 and slickensided serpentine occurs in association with ophicalcite. At 

 Ty Newydd altered enstatite is found in addition to the serpentine 

 derived from olivine, and the rock yielded to Mr. HOUGHTOX the following 

 analysis : 



Si0 2 ... ... ... ... 38-62 



Al.O, ... ... ... ... 4-15 



Fe 2 3 ... ... ... ... 5-21 



FeO ... ... ... ... 4-34 



MnO ... ... ... ... tr. 



CaO ... ... ... ... tr. 



MgO ... ... ... ... 33-83 



Na,0(K 8 0) ... ... ... -70 



H 2 ... .. ... ... 12-52 



99-37 



It appears, therefore, that the Aiiglesea serpentines in many respects 

 bear a close relation to those of Cornwall. They give distinct evidence in 

 places of having been derived from olivine rocks, and they occur in intimate 

 relation with gabbro which is often foliated and sometimes appears to pass 

 over into a true schist. The crumpling in the surrounded rocks, the foliation 

 in the gabbro and the crushed and slickensided aspect of the serpentine in 

 certain places all bear testimony to the fact that the rocks of the district have been 

 profoundly modified by regional metamorphism. The precise relations of 

 the serpentine to the surrounding schists are not yet explained. 



Can-ick, Ayrshire. The rocks of this district have been described by 

 Dr. J. GEIKIE /3) and Professor BOXXEY. (4) The following description is 



(1) Memoirs of the Geol. Survey, Vol. III. 



(2) Q.J.G.S., Vol. XXXVII., 1881, p. 40. 



(3) Q.J.G.S., Vol. XXIL, 1866, p. 513. 



(4) Q.J.G.S., Vol. XXXIV., 1878, p. 771. 



