82 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



fossils were interstratified in the series of rocks forming the most 

 northerly of his metamorphic areas in Anglesey, and he regarded 

 the metamorphic rocks of that district as altered Llandeilo or Bala 

 beds *. In the centre of the island he believed that a considerable 

 extent of Silurian rocks had been metamorphosed into gneiss and 

 mica-schist f. 



These views have been impugned by Professors Hughes 4: and 

 Bonney §, Drs. Hicks |j and Callaway ^, the Eev. J. F. Blake **, 

 and others. There is a general agreement among these writers that 

 the rocks coloured on the Survey map are not altered Cambrian, but 

 are of pre-Cambrian age. The most opposite opinions, however, have 

 been expressed as to their nature and order. The latest view is that 

 expounded by Mr. Blake, who has erected the so-called " pre- 

 Cambrian" rocks of Anglesey into a new geological system to which 

 he has given the name of " Monian." 



Without attempting here to collate or criticize these diverse judg- 

 ments, let me frankly say at once that in denying the existence of 

 pre-Cambrian rocks in Anglesey, and in endeavouring to account for 

 all the schists by the metamorphism of Cambrian and Silurian 

 strata, my predecessor was, in my opinion, mistaken. I have little 

 doubt that were he able once more to ramble over those hills and 

 shores which he knew and loved so well he would himself, in the 

 light of present knowledge, freely admit the error. 



As no two observers agree in their reading of the pre-Cambrian 

 rocks of Anglesey, I shall content myself with a brief statement of 

 the main points as to which I believe the work of the Geological 

 Survey requires amendment. 



The rocks coloured on the map as altered Cambrian and Silurian 

 embrace, I think, at least three totally distinct series. The whole of 

 these have been claimed as pre-Cambrian. One of them, as I shall 

 have occasion to show in a later portion of this Address, is certainly 

 Lower Silurian, and was correctly so interpreted, in part at least, by 



* Op. cit. pp. 224, 236, 240. t Op. cit. p. 242. 



\ Quart. Journ. Geol. Soc. vols, xxxiv. (1878) p. 137, xxxv. (1879) p. G82, 

 xxxvi. (1880) p. 237, xxxviii. (1882) p. 16 ; Brit. Assoc. Eep. 1881, pp. 643, 

 644 ; Proc. Camb. Phil. Soc. vol. iii. pp. 67, 89, 341. 



§ Quart. Journ. Geol. Soc. vol. xxxv. (1879) pp. 300, 321 ; Geol. Mag. (1880) 

 p. 125. 



II Ibid. vols, xxxiv. (1878) p. 147, xxxv. (1879) p. 295 ; Geol. Mag. (1879) 

 pp. 433, 528. 



^j Ibid. vols, xxxvii. (1881) p. 210, xl. (1884) p. 567. 



** Ibid. vol. xliv. (1888) p. 463. 



