28 PALEOZOIC TIME. [CHAP. III. 



quite possible that the Malvern Hills were part of the 

 southern border of this land. 



The larger part, if not the whole, of Wales formed part 

 of the Ordovician sea, and in this area the Cambrian sedi- 

 ments are succeeded by a thick series of comparatively 

 deep-water rocks, though they certainly were not formed 

 at any great distance from land. The succession consists 

 of (1) the Arenig series black slates and flags, from 3,000 

 to 4,000 feet thick, with the addition of much volcanic 

 material in the north-west of Wales; (2) the Llandeilo 

 series another group of black slates and nags, with a thin 

 limestone, in South Wales ; (3) the Bala series a more 

 variable group, consisting of shales and sandstones, with 

 two bands of limestone, the whole from 4,000 to 6,000 feet 

 thick. 



As these Ordovician strata occur in full force on both 

 sides of the Pembrokeshire Archaean axis, it is probable 

 that this was completely submerged and covered by these 

 sediments. 



In Shropshire the same complete series is found on the 

 western side of the Longmynd ridge, but in the Caradoc 

 district, on the eastern side of that ridge, the Arenig 

 and Llandeilo series are absent, sandstones of Bala age, 

 having a conglomerate at their base, resting on the local 

 representative of the uppermost Cambrian. 



Fig. 1 is an ideal section, drawn for the purpose of 

 showing the possible underground geology of the midland 

 counties, for it is absolutely necessary to form some con- 

 ception of this before we can draw any inferences regarding 

 the probable position and extent of the land area which 

 seems to have existed over the centre of England in Ordo- 

 vician times. From the section it is seen that the Caradoc 

 sandstones are supposed to thin out beneath the Silurians 

 against the pre-Cambrian rocks, and that there is reason 

 to suppose that they were never deposited over that part of 



