464 HEV. J. r. ELAKE OK" THE 



Pee-Cambeiai? Age of Akglesey Eocks. 



It may well be considered that recent literature Las already 

 proved this point, so far as the direct evidence of unconformity is 

 concerned. This evidence may he of two kinds, that derived from 

 actual stratigraphical relations, and that derived from included 

 fragments. Of the former kind we have an example in Prof. 

 Hughes's admii^ahle description of the basement-beds of the over- 

 lying series *. Of the latter kind, are the statements by several 

 authors that the conglomerates near Llanfaelog contain a large pro- 

 portion of pebbles derived from the neighbouring rocks f- The 

 bearing of these observations depends on the age of the conglome- 

 rate. JN'ow on this matter Sir A. Eamsay says, on the authority of 

 llr. Salter, that the " fossiliferous grits do not necessarily represent 

 the very base of the Eala " J. Prof. Hughes, however, has shown 

 that the fauna may be more correctly referred to the Arenig §. He 

 would even introduce the Tremadoc, though Dr. Callaway has, I 

 think, conclusively shown that this is not warranted by the facts ||. 

 Even so, however, another statement by Sir A. Eamsay remains 

 untouched, that " no Lingula-flags have yet been detected in the 

 country, and it is probable that they have been unconformably 

 overlapped before reaching this northern area . . for they are reduced 

 .... between Merionethshire and Llanberis, and seem to have almost 

 or altogether thinned away before reaching Bangor." 



The whole of the above-mentioned observations, therefore, only 

 go to prove that the rocks in question are Pre-Ordovician, a result 

 freely admitted by Sir A. Eamsay as perfectly consistent with their 

 Cambrian age ; though he undoubtedly regarded the gi'anite as of 

 Post-Cambrian, though of Pre-Eala age, which is all that the con- 

 glomerates, if themselves of Bala age, would prove. It would seem 

 as if misunderstanding had been introduced here by the use of the 

 name Cambrian for strata which Murchison had already defined as 

 Lower Silurian, at a time when the geology of " Cambria " was 

 stiU in confusion, and which have a distinct and unconformable 

 base-line. Thus, the Pre-Cambrian age of the Anglesey rocks is 

 not proved by these writers. 



Prof. Bonney ^, however, in a recent paper does supply the needful 

 proof, though he appears to rely more on differences in amount of 

 metamorphism than on the stratigraphy. He describes the section 

 now exposed in Baron-Hill Park, near Beaumaris. Here, in the 

 roadside cutting, the schistose masses are seen to be suddenly re- 

 placed by a group of rocks which may with perfect safety be iden- 

 tified with some of the Cambrian rocks of Bangor, which lie below 

 the felsitic conglomerate. They consist, as Prof. Bonney states, of 

 grits, porceUanites, and halleflintas, and, at the summit, of a red 



* Quart. Journ. Geol. Soc. vol. xxxviii. 



t Callaway, Quart. Journ. Geol. Soc. toI. xxxvii. ; Hicks, ibid. vol. xl. 



+ Mem. Geol. Surv. vol. iii. 1866, p. 193. 



§ Quart. Journ. Geol. Soc. vol. xxxvi. 



II Ibid. vol. xxxvii. ^ Ibid. vol. xxxix. 



