SILURIAN ROCKS OF NORTH WALES. 157 
Corwen Grits, but I have not been able to identify them with 
any certainty as I obtained from those beds only an Orthis and 
a few other indeterminable fragments of fossils. I know, how- 
ever, that there are in that district several bands of sandstone 
- in the Bala Beds which might easily be confounded with the 
Corwen Grit, especially when somewhat decomposed. A little 
creek cuts off the Castle from the hill on the South, along the 
estuary at the base of which there is a cliff which shows the 
succession of the lower part of the Silurian Rocks very clearly. 
The most northern part, under the hedge by the timberyard, 
may, perhaps, be more conveniently bracketed with the base- 
ment series. (Ga. & Go.) 
The Series, though varying in details, is identical in general 
character. It consists of conglomerate, grit, sandstone, pale 
felspathic shaley mudstone, and black bands with graptolites. 
Sometimes the black bands with graptolites were absent; somo- 
times the pale slates; sometimes the conglomerate ; while in 
other districts it was the sandstone that was most rarely present. 
When all are present the order is :— 
Ga. Pale slates passing down into 
Gb. Black shales with graptolites. 
Gc. Sandstone, grit, and conglomerate ; 
and if we turn to the details of C & D we shall find that each 
character is exactly represented in one or other of the North of 
England Sections. 
The basement beds can be traced at intervals from Corwen 
by the shooting box, known as Liberty Hall, under Moelygwynt, 
where pale slates are seen dipping 10° N.N.E. with a cleavage 
65° N.N.W. ‘The Caer Drewyn Grits form further to the East 
a feature which can be followed from Penyglog to Moel Ferna, 
and is probably represented by the grit running along the hill 
about }-mile North of Llansantffraid-glynceiriog. South of 
that place the basement beds are again seen, as I have pointed 
out on a former occasion (Q.J-G.S 1877, PP 210) 21 1) running 
along the line of the tramway near Ponthafodgynfor, and then 
S.W. up Fronfrys towards Tynyfron. The basement beds are 
here somewhat irregular and variable, consisting generally of 
alternations of bands of limestone and fine sandstones with 
wavy lines of bedding at the base. ‘he calcareous portions 
weather into a brownish or gingerbread coloured rock, as in the 
case of the Hirnant Limestone and other calcareous beds of this 
age; as for instance in Westerdale in Yorkshire (see p. 148.) 
Té must be borne in mind that these basement beds are 
sometimes very full of pyrites, the decomposition of which 
helps to produce the rusty appearance so common in the 
weathered rocks at this horizon. 
It will be obvious from a comparison of the two series that 
the correspondence between the subdivisions in the Lake 
District and North Wales is too close to be referred to accident. 
C2 
