72 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the bare Longmynd rocks without any intermediate beds at all. The 

 Pentamerus limestone, too, in the same region, frequently overlaps 

 the conglomerate beds, so that there may be a slight amount of un- 

 conformity between each of these strata in their turn. But the 

 connexion between the organic remains of the conglomerates and 

 those of the Pentamerus limestones is perfect, and the latter appear 

 gradually to lose their peculiar species, and to graduate upwards 

 into the Wenlock shale. This may be accounted for, however, by 

 the land gradually sinking during the formation of these beds, without 

 supposing any great disturbance or long interval of time, and hence, 

 as above stated, there is very little change in the fossil contents, 

 except what may be referred to a variation in the depth of the sea. 



Between these strata, however, and the sandstone formerly called 

 " Caradoc sandstone,'" there is no true passage, nor any similarity 

 in fossil contents in the country under review ; and it is evident 

 that they can no longer be classed under the same name. The rocks 

 east of Caer Caradoc, formerly considered as typical Caradoc, are the 

 equivalent of the Meifod and Bala rocks, and of their upper and 

 middle portions only. The overlying strata, on the contrary, are 

 identical (at least in part) with the arenaceous beds described by 

 Prof. Ramsay (vol. iv. p. 299) as lying at the base of the Wenlock 

 shale at Builth, and with the sandstones of Presteign, May Hill, and 

 Malvern, to which Prof. Sedgwick has applied the term " May Hill 

 sandstone." Whether the Caradoc sandstone of the Welsh counties 

 {supra, vol.iv. p. 294*) be identical with these overlying beds, as 

 suggested from fossil evidence by Professors Sedgwick and M'Coy, is 

 not yet certain, from the want of sufficient fossil data ; but so far as 

 the collections yet made in these barren tracts may serve, the fossils 

 agree well with this view, scarcely any of the true Bala fossils being 

 found in them ; and, on the other hand, many common Upper Silu- 

 rian fossils are plentiful there. 



Should further examination prove this to be the case, the name 

 " Caradoc sandstone " might still be retained for this large interme- 

 diate formation, several parts of which have been constantly so named 

 in various works ; and the " Pentamerus limestone," characterized 

 by species which are plentifully found in bedsf below and above this 

 " Caradoc " formation, is thus linked on to the older strata, and at 

 the same time forms the bed of passage from the Lower to the Upper 

 Silurian rocks. 



Summary. 



The conclusions to be drawn from the foregoing data may be thus 

 shortly stated. The rocks east of the Longmynd hitherto known as 



* At p. 296, the conglomerates around the Longmynds are identified with the 

 Welsh Caradoc sandstone, but they were not separated from the rocks east of 

 Caer Caradoc. 



t The sandstones referred to in the memoir by Prof. Ramsay, before quoted, as 

 occurring 1000 to 1500 feet below the Caradoc sandstone of North Wales, are full 

 of the characteristic Pentamcri, Atrypce, &c. of these uppermost beds. All the 

 Pentameri abound there, and Airypa rdicularis, Holopclla cancellata, &.c. are 

 frequent fossils. Atrypa hemisphcerica is more rare. 



