The Rev. Prof. Blake— Base of the Sedimentary Series. 359 



writings of Murckison, there was nothing Precarnbrian in this county. 

 The whole of the Longmynd rocks from the Slopes of Caradoc to the 

 Stiper stones was one continuous sequence of Cambrian rocks, of 

 which no base was seen, and the volcanic rocks of Caradoc and the 

 Wrekin were intrusive greenstones affecting both Ordovician and 

 Cambrian strata. The first blow to the correctness of this interpre- 

 tation came from Mr. Allport, who showed that some part of the 

 "greenstones" in the Wrekin district were rhyolitic lava-flows, 

 and another part in the Wrekin range itself consisted of bedded 

 volcanic ashes. This was followed up by Dr. Callaway, who proved 

 that beneath the Tremadoc (Shineton) shales were other Cambrian 

 rocks lying unconformably on and therefore younger than the 

 Wrekin rocks. Thenceforth it was clear that these volcanic rocks 

 are in some sense Precarnbrian. and the same thing was proved with 

 regard to Caer Caradoc. 



This was the starting point for a search after further Precarnbrian 

 formations in the district, and first it was noted by Dr. Callaway 

 that in the Ercal there is a mass of coarsely crystalline rock of acid 

 type and without foliation, associated with the volcanic rocks of the 

 Wrekin. It seems to have been more or less assumed that this was 

 not an intrusive rock ; and under the influence of the theory that 

 ordinary sediments became by metamorphosis massive crystalline 

 rocks, it was considered, from some peculiarities in its structure, to 

 be of such an origin and of earlier date than its surroundings. At 

 the same time, some small patches of foliated rock were found at the 

 south end of the Wrekin, on Primrose Hill, and these were referred 

 to the same period as the Ercal rock, and both were correlated with 

 the rocks of the Malvern. It may here be noted that this interpre- 

 tation involves the assumption that in the same massif there can be 

 ordinary sediments converted into massive crystalline rocks, and 

 massive crystalline rocks converted into gneisses, at approximately 

 the same epoch. The superior antiquity of these crystalline rocks 

 was thought to be proved, however, by the discovery at Charlton 

 Hill of a conglomerate, apparently forming part of the volcanic 

 series — and in such situations as to be obviously older than the 

 quartzite — which contained pebbles of similar crystalline rocks. A 

 third group of micaceous schists was also indicated near Rushton, 

 whose relation to all other rocks of the neighbourhood was obscure. 

 The Precarnbrian age of all these was evidenced by their relations 

 to the quartzite, and the Longmynd conglomerates containing 

 their fragments. A little later a series of isolated patches on the 

 western border of the Longmynd, which were for the most part 

 coloured as intrusive greenstone on the Survey map, were examined 

 by Dr. Callaway and considered to be Archeean, partly because some 

 of them were like the old Wrekin rhyolites ; partly because traces 

 of bedding were to be found in others ; and partly because a con- 

 glomerate in the Longmynd series in one place dipped away from 

 the supposed ArcliEean mass, and contained some rhyolitic pebbles. 

 The same evidence was thought to prove a synclinal in the western 

 part of the Longmynd, by which the lower beds near their junction 



