ARCH^AN. 37 



diorites, comprise granitoid gneisses, hornblendic and micaceous 

 schists, etc. Dr. Callaway has grouped the beds as follows : ^ — 



Pebidian .... Hornstones of Herefordshire Beacon. 



iDimetian, with associated quartz-felsites and 

 halleflintas (Arvonian), passing down into 

 Lewisian. 



Ahberley Hills. — The Rev. W. S. Symonds has suggested that the 

 'syenitic' rocks seen near Hartley, and also between Berrow Hill 

 and King's Common, along the line of the Abberley Hills, may be 

 of Pre-Cambrian age. 



WALES. 



In 1838 Sedgwick grouped the "crystalline slates" of Anglesey 

 and the south-west coast of Caernarvonshire as Pre-Cambrian 

 (Protozoic) ; "^ but they were subsequently regarded as altered 

 Cambrian by Sir A. C. Ramsay, In 1872, however, the Rev. W. S. 

 Symonds recalled attention to the subject, remarking that these 

 crystalline rocks are not simply altered portions of the grits and 

 slates which form the base of the Cambrian rocks in the counties 

 of Merioneth and Caernarvon, and that they should be classed as 

 Pre-Cambrian.^ 



In 1864 Dr. Henry Hicks arrived at the conclusion that in North 

 Pembrokeshire the " intrusive syenite and felstone " (marked on 

 the Geological Survey Map) were portions of an old Pre-Cambrian 

 ridge or island. His earlier views were worked out in conjunction 

 with Mr. J. W. Salter,* while his later conclusions have been 

 developed from long-continued personal labour, aided by micro- 

 scopical investigations carried on by Prof. T. G. Bonney and Mr. 

 Thomas Davies. As the divisions made in the Archaean rocks of 

 St. Davids have been followed out by some observers in other 

 localities, it will be well to describe them in detail. 



In 1876 Dr. Hicks proposed to divide the Pre-Cambrian rocks of 

 St. Davids into two distinct series. He introduced the local name 

 of Dimetian for the lower series, Dimetia (or Demdcc) being the 

 Roman name for a kingdom which included, or for a Celtic tribe 

 which inhabited, this part of Wales ; and the name Pebidian for 

 the upper series, Pebuh'auc (or Pebidiog) being the name of t^e 

 division or hundred in which these rocks are chiefly exposed. In 

 1 87 1 he introduced a third division intermediate between the two 

 others, which he termed Arvonian, from Arvonia, the Roman name 

 from which Caernarvon is derived.* 



^ Q. J. xxxvi. (Proc.) 3, and 538. 



" Proc. G. S. ii. 684. 



^ Records of the Rocks, 1872, p. 28. 



* G. Mag. 1864, p. 289, 1865, p. 430. 



* Q. J. xxxiii. 230 ; xxxiv. 153; xxxv. 285; xl. 507; and G. Mag. 1S78, 

 .461. See also Harkness and Hicks, Q. J. xxvii. 388, 396. 



