300 PROCEEDINGS OF THE GEOLOGICAL SociETY. ([Apr. 5, 
2. Sketch of the Structure of the country extending from CADER 
Ipris to Moet S1asop, Norra Wates. By J. Beete JuKEs, 
F.G.S., and Atrrep R. Setwyn, of the Geological Survey of 
Great Britain. 
[Abstract by the Authors. ] 
Tue rocks are arranged into the following groups, of which the 
names are only provisional, and the thicknesses assigned from rough 
estimation. In the ascending order :— 
A. The Barmouth and Harlech sandstones, 3000 feet. A mass of 
quartzose sandstone and conglomerate, with some beds of blue 
and purple slates, and occasionally trap rocks. 
No organic remains discovered in this group. 
B. The Trappeean group, 15,000 feet: subdivided into— 
B 1. Blue and grey schistose slates and flagstones, inter- 
stratified with many beds of a grey calcareo-feldspathic “as 
often crystalline, together with feldspathic trap and greenstone ; 
the slaty rocks predominating. 
B 2. Great masses of feldspar-porphyry and. some green- 
stone, with feldspathic trappeean “‘ash”’ arranged in beds a few 
inches or many feet in thickness. Interstratified with these, and 
passing into them (especially into the ash) by almost impercep- 
tible gradations, are many beds of black slate, forming often 
irregular and apparently lenticular-shaped masses. In some 
parts of B 1, Lingule are found in great abundance, and a few 
other fossils. In B 2 Lingulee and Graptolites also occur, but 
not very abundantly. 
C. The Bala group, 9000 feet: subdivided into— : 
C 1. Black slates of variable thickness, very fine-grained, 
brittle, and frequently having their true lamination or stratifica- 
tion entirely obscured by cleavage and numerous joints. 
C 2. Grey, fine-grained, arenaceous slate-rock, often passing _ 
into a hard, compact, splintery gritstone; in its lower portion 
are one or two beds of trappzean ash, sometimes crystalline, 
sometimes flaky and sometimes brecciated, often highly calea- 
reous. About its centre is one thin bed of impure limestone 
(Bala limestone), and sometimes, but very rarely, another little 
band in its upper portion (Hirnant limestone). Organic remains 
are very rare in C 1; but in C 2, as is well known, are very 
abundant and in great variety. 
The top of the Bala group sometimes passes into black slates and 
shales with beds of sandstone, which are covered by sandstones be- 
longing to the Caradoc sandstone group. The latter however gene- 
rally overlaps or rests otherwise unconformably on the beds of the 
Bala group. 
The Barmouth and Harlech sandstones (A) occupy the coast be- 
tween those two places, and extend inland as far as the Dolgelly and 
Trawsfynnydd road, includmg the ranges of Rhinog Fawr and Y 
Craig ddrwg. Neglecting mimor undulations, the beds of this tract 
dip on every side from its central portion except towards the sea. Be- 
