276 PEOF. T. G. BONNEY AND MISS C. A. RAISI^' ON [May 1899, 



19. On, Yarteties of Serpentine and Associated E,ocks in Anglesey. 

 By Prof. T. G. Bonney, D.Sc, LL.D., V.P.ll.S., F.G.S., and 

 Miss C. A. Baisin, D.Sc. (Bead February 22nd, 1899.) 



[Plate XXIII.] 



Contents. 



Pnge 

 I. General Description 276 



(1) Mainland of Anglesey — south of Vallej Station. 



(2) ,, „ near the Lakes. 



(3) ,, „ south of Llanfair-vu-neubwU Inlet. 



(4) Holyhead Island — Rhoscolyn Parish. 

 II. Serpentine. 



(a) Macroscopic Characters 280 



(1) Normal Varieties. 



(2) Banded Serpentine, 



(3) Variolitic Serpentine. 



(/3) Microscopic Characters 284 



(1) Normal Varieties. 



(2) Variolitic Serpentine. 



III. ' Ophicalcite ' 289 



IV. Other Intrusive Rocks 2iJ0 



(1) Pyroxenites, Enstatite-rock. etc. 



(2) Gabbro. 



(3) Porphyrite (?). 



(4) Greenstones. 



V. Actinolite-tufts in Rocks near Junctions 294 



VI. Chlorite-rock and Talc-schist 2U7 



VII. Effects of Pressure ; Age of the R j»cks 300 



I. General Description.^ 

 (1) Mainland of Anglesey — south of Valley Station. 



On the eastern side of the 'strait'^ is the gabbro at Graig-fawr 

 described in a former paper by one of the present authors.^ A 

 serpentine, there indicated as ' about 70 yards to the north ' of this 

 mass, has been quarried further,"* and parts of the rock exhibit a 

 slightly variolitic character. The junction of schist "with serpentine 

 or ' ophicalcite' noticed and figured {op. cit. p. 41, fig. 1) is in a 

 low cliff by the shore almost due south of Graig-fawr and near a 

 boss of variolitic serpentine, described on p. 281. This junction 

 is not easy to interpret ; but further study of the rocks affords some 



^ I am bound to state that, though I have been once or twice on the ground 

 eince 1880 (when n>y paper was written), the whole of the laborious field-work 

 lor the present communicatiou has been done by Miss Raisin, but that we are 

 jointly responsible for the examination of specimens and the interpretati )n of 

 results.— T. G. B. 



^ We apply this term to the water separating Holyhead Island from 

 Anglesey. In the district it is called the ' river.' 



3 T. G. Bonney, Quart. Journ. Geol. Soc. vol. xxxvii (1881) p. 40. The 

 gabbi'o is there described as ' near Ty-newydd ' (as shown on the I -inch map). 

 Tiie names in the present description are taken from the 6 inch Ordnance 

 Survey map. 



^ The mas still more recently has been quarried, and carted away. 



