13 



lohata, Leptcena sericea, duplicata and depressa, and Spirifer radiatus. 

 This bed is much broken, and difficult to trace, but its general direc- 

 tion from Y-Garnedd, 1^ mile east of Bala, to the upper valley of the 

 Cowarch, is nearly N.N.E. The line of limestone laid down, both 

 in Mr. Murchison's and Mr. Greenough's Maps, is compounded of 

 the beds No. 2. and No. 4. 



5. Grey slaty grits. — Occasionally streaked or passing into brown, 

 very hard ; well seen on both sides of the lake of Bala and in the 

 upper part of the valley of the Twrch ; usual dip E.S.E. 45°, but 

 much disturbed about the foot of the lake : the upper bed contains 

 Orthis canalis, anomala and vesperiilio. In the lower part is a bed 

 thirty or forty feet thick of impure grey limestone with many frag- 

 ments of Trilohites and other organic remains, among which Mr- 

 Sharpe recognised Bumastus Barriensis, Trinucleus Caractaci, Illanus 

 crassicauda, Orthoceras approximatum, and Lituites cornu-arietis. This 

 bed was only seen near Rhiwlas and Llan-y-ci, on the north-west of 

 Bala. The grits below the limestone are similar to those above, and 

 contain Orthis canalis and vespertilio, Leptcena sericea and Asaphus 

 tyrannus. The whole exceeds 500 feet in thickness. 



6. Rotten grey clay-slate, weathering to brown, forming the 

 moor between Bala and Arenig, and exposed where Cwm Croes joins 

 the valley of the Twrch : supposed to be 500 feet thick. 



7. Dark blue slate, of poor quality, covers the eastern flanks of 

 Arenig and Arran Mowddy, quarried at Blaen-y-cwm, where the 

 beds dip N.E. 35°, and the cleavage dips E.N.E. 55°: the lowest bed 

 of the series. 



As the Bala beds are quite unconnected with the Cambrian rocks 

 of the Berwyns, and are only overlaid by Upper Silurian deposits ; 

 as most of their oi-ganic remains are known Lower Silurian species, 

 and as the total thickness, of the whole series is about the same as 

 has been assigned by Mr. Murchison to the Lower Silurians, Mr. 

 Sharpe concludes that they are the exact equivalents of the Lower 

 Silurian formation, and do not carry the series down below the beds 

 described by Mr. Murchison. Mr. Sharpe considers it as easy to 

 prove their identity with the Caradoc sandstone as with the Llandeilo 

 flags, and again endeavours to show that these must be regarded as 

 the same formation under diff^erent names. This classification re- 

 places the dark blue limestones of Bala and Coniston, on the same 

 parallel from which they were separated when Professor Sedgwick 

 adopted Mr. Marshall's view of the Silurian age of the Coniston 

 limestone, but left the Bala limestone in its erroneous position as 

 part of the Upper Cambrians. 



Mr. Sharpe adds comparative tables of the Silurian system as ex- 

 hibited in three different districts : — in Westmoreland, as observed 

 by himself; in Denbighshire and Merionethshire, the upper part 

 taken from Mr. Bowman's memoirs, the lower added by himself; 

 and in Shropshire, &c., as described by Mr. Murchison ; ijut he de- 

 fers the full comparison of these till he lays before the Society the 

 conclusion of his remarks on Westmoreland. 



Mr. Sharpe hopes that he has done away with an objection often 



