Dr. C. Catiaway—Pre-Cambrian Geology of Anglesey. 123 
Fie. 3.—Plan of the group between Ty Croes and Gwalchmai. 
Se 
Per carmgiog 
&S 
i Ty Croes.5. tation 
Scale—-one inch to the mile. 
C.—Assoocration or Voxtcantco Rocks wirH THE GRaNiTorp GRovP. 
(a). Section at Ty Croes.—Dr. Hicks founds his Anglesey succes- 
sion upon a section at Ty Croes.' Assuming the granitoid band as 
the base, he finds to the E. an exposure of hiilleflinta, and this he 
places above the granitoidite, and calls “ Arvonian.” Further to the 
K., he comes upon green schist with an easterly dip, which he regards 
as the summit of the series, and identifies as Pebidian. To this 
order I am compelled to take serious objection. 
In order to ascertain the true succession, I ran a series of sections 
in zigzags across the three zones, for six miles on the strike to the 
N.E. A few of the most decisive results are here given. I take the 
localities from S.W. to N.E. 
At Pen y carnisiog, one mile N.E. of Ty Croes, the Dimetian 
clearly dips to the N.W., and one band of it passes up into quartz- 
felsite (Note 4, p. 125), without any line of separation. 
Between Ty Croes and this point, the “ Arvonian ” hilleflintas and 
quartz-felsites form a well-marked zone between the Dimetian and 
the schists. As the Dimetian dips to the N.W., it is difficult to see 
how the “ Arvonian” can dip to the S.H.; and as bands of quartz- 
felsite of the ‘‘ Arvonian ” type are interstratified with the danse 
1 Quart. Journ. Geol. Soc. vol. xxxv. p. 302. 
