English Stratified Rocks inferior to the Old Red Sandstone. 303 



Though abounding in calcareous matter, it has no organic remains. 

 {Lower Cambrian system). 



(3.) A great series, exjianded through Westmoreland and parts of 

 Lancashire and Yorkshire. Itis based on calcareous slates, passing into 

 limestone, and full of organic remains, and in its lower division are fine 

 roofing slates, but less crystalline than those of the preceding group. 

 Its upper division (not however separable by any very distinct zoologi- 

 cal or mineralogical characters from the lower) abounds in arenaceous 

 flagstone, coarse quartzose greywacke, coarse slates with imperfect 

 cleavage, and not fit for use, and the series is incomijlete, being cut 

 ofi^ by the unconformable deposits of old red sandstone and carboni- 

 ferous limestone. Distinct beds of limestone are almost wanting in 

 this upper division, and organic remains are very rare, but they ap- 

 pear here and there in very thin bands among the coarse siliceous 

 slates. Provisionally, the lower division is placed in the Upper 

 Cambrian system, and the upper division in the Silurian system ; but 

 without being separable into any further clear subdivisions. This 

 great group (No. 3.) does not appear on the north side of the 

 mineral axis of Cumberland, as was represented in the early geolo- 

 gical maps. 



SECTIONS OF NORTH WALES, &C. 



The author next discusses a series of sections illustrating the 

 structure of North Wales. One is drawn from the Menai Straits, 

 in a direction about E.S.E., so as to cross theBerwyn chain and end 

 in the carboniferous series near Oswestry. The others are drawn 

 from the Berwyn chain to different parts of the carboniferous lime- 

 stone range on the north side of Denbighshire. The greater por- 

 tion of the first section crosses the older beds (the Cambrian System) 

 which strike towards the N.E. The other sections intersect the 

 upper series (Silurian System) which strike towards the N.W., 

 passing (in some places unconformably) round the beds of the older 

 system. From a consideration of the whole evidence the rocks are 

 grouped in the ascending order as follows. 



(1.) Chlorite slate, quartz rock, and mica slate of Anglesea and 

 Caernarvonshire. These are placed on the parallel of the first class ; 

 and nothing is discovered in the section that is perfectly analogous 

 with the Skiddaw slate, or first Cumbrian group, above described. 



(2.) The old slate series of Caernarvonshire and Merionethshire, 

 alternating indefinitely with bands of porphyry and felspar rock; 

 many parts absolutely identical in structure with the second Cum- 

 brian group above-described. It is of enormous but unknown thick- 

 ness, and is bent into great undulations, the anticlinal and synclinal 

 lines of which are parallel to the strike of the chain. Through wide 

 tracts of country it is without fossils ; but at Snowdon and Glider 

 Fawr, encrinites, corals, and one or two species of bivalves have 

 been discovered in it. It ends with the calcareous beds which range 

 from Bala to the neighbourhood of Dinas Mowddy. This is called 

 the Lower Cambrian System. 



(3.) The next group (the Upper Cambrian System) commences with 



