474 Prof. Sedgwick on the May Hill Sandstone, 



before the Geological Society of London, Nov. 3, 1852) the fol- 

 lowing sections were discussed : — 



The first section was from the Cambrian and Silurian rocks on 

 the line of the Holyhead road, west of the Berwyns, and was as 

 follows {supra, fig. 1 . p. 306) : — 

 5. Carboniferous series. 



4. Devonian series, vei*y degenerate, and unconformable to the 



Denbigh flag. 



3. Denbigh flag, &c. (Wenlock and Ludlow). 



2. May Hill sandstone, of great thickness, and ending in a 



conglomerate. Unconformable to the Cambrian rocks. 



1. Cambrian rocks of the Bala group. 



The second section was taken from the sequence north and 

 south of the valley of the Dee, near Llangollen (supra, fig. 3. 

 p. 30G). 



5. Carboniferous rocks. 



4. Denbigh flag. (No. 3 of fig. 3. p. 306.) 



3. Upper Bala group, with two bands of limestone. 



2. Alternations of slate and porphyry, trap-shale (schaalstein) , 



&c., with many Cambrian fossils. 



1. Beds of dark shale, grits, flags, &c., in which fossils gra- 



dually disappear. 



Here there is no apparent unconformity, and the stage No. 3 

 might be almost said to pass into the stage No. 4; but the 

 absence of the May Hill sandstone and conglomerate of the pre- 

 vious section proves that No. 4 has been brought over No. 3 by 

 a great overlap, and that the section is therefore imperfect. 



The third section was from Mathyrafal near Meifod {supra, 

 p. 306. fig. 2). 



4. Wenlock shale, &c. (No. 3 of fig. 2. p. 306.) 



3. Beds of shale with many fossils (a good Cambrian stage). ^ 



2. Beds of limestone, coarse calcareous conglomerate, &c. 

 1. Fossiliferous series of the Meifod Hills, &c. 



Here Nos. 1, 2 and 3 represent a peculiar development of the 

 Upper Bala groups,. and are collectively of great thickness. 



Between Nos. 3 and 4 there is an obvious discordancy of posi- 

 tion, and the May Hill series is wanting. It is probably over- 

 lapped by, and buried under, the Wenlock shale ; and between 

 Nos. 3 and 4 there was, so far as we saw, no interchange of cha- 

 racteristic Cambrian and Silurian species *. 



The 4th, 5th and 6th sections from Norbury, the banks of the 

 Onny and Shineton (where the Caradoc sandstone approaches 



* I may remark, as I have done in a j)revious paper, that all the beds 

 below the May Hill sandstone are here called Cambrian, whatever may 

 have been their supposed sectional place in the " Silurian System." 



