450 S. ALLPORT ON PITCRSTONES AND PERLITES PROM 



resemblance whatever to greenstone or any other rock of the basic 

 series. In a large quarry at the south end of Lawrence Hill thick 

 beds of volcanic ash are seen dipping in a northerly direction, at an 

 angle of 55°. Like all the rocks of the range, they have been greatly 

 disturbed and fractured ; but the strike of the beds is clearly across 

 the ridge. They here consist of several alternations of coarse and 

 fine material, the whole of which have been highly indurated and 

 otherwise altered. These beds are covered by masses of altered pitch- 

 stones and felsites, which are well exposed on the south slope of the 

 hill, on its steep northern face, and also on the opposite crags of Ercal 

 Hill. Returning southwards to the narrow ravine which separates 

 Lawrence Hill from the Wrekin proper, the ash-beds are again 

 exposed in the precipitous face of the latter ; the bedding is here 

 massive or obliterated, although the fragmental character of the 

 rock is still perfectly distinct. Further southwards, along the 

 summit of the ridge, beds of the coarser ash are again seen, and may 

 be traced at intervals for a distance of more than six hundred 

 yards. From this point to the south-western termination of the 

 ridge there are comparatively few exposures of rock ; and these 

 consist of compact reddish-brown felsite or altered pitchstone — the 

 compact felspar of Murchison and others. 



On the summit of the ridge, at a short distance to the north of 

 the wood, there is a slight rounded elevation formed by a mass of 

 altered dolerite, which appears to be intrusive ; and in the quarry 

 at the south end of Lawrence Hill there are two dykes : one, on the 

 east side, is 12 ft. wide ; the other is 14 ft. at bottom, cuts through 

 the lower ash-beds, then bifurcates, and the two diverging branches 

 rise through the upper beds to the surface. The rock forming both 

 dykes is a highly altered basalt. 



It is evident, therefore, from an examination of this part of the 

 ridge, that the axis is not formed by a continuous band of green- 

 stone, as hitherto represented, but that in reality it here consists of 

 an extensive series of regularly stratified agglomerates and ashes 

 alternating with amorphous masses of altered pitchstones or felsites. 



The general strike of the surrounding strata is north-east ; and the 

 central ridge is flanked by masses of quartzite, which are laid down 

 on the map as Caradoc Sandstone, altered by the supposed intrusive 

 greenstone. Whether these rocks be altered Caradoc strata or not, 

 they are clearly unconformable to the stratified ash-beds of the 

 ridge ; and I think there is some reason to believe that the latter 

 belong to the older contemporaneous volcanic series so extensively 

 developed in the Lower-Silurian district of Salop and Radnor. 



The mass of trap lying to the west of Wellington and the Wrekin 

 is a hard rock which has suffered less from denudation than the soft 

 Triassic sandstones by which it is surrounded ; it forms a low hilly 

 tract, usually presenting rounded or flat surfaces, on which several 

 large boulders of granite and felstone have been stranded. These 

 erratics appear to be quite similar in character to those forming the 

 well-known and far more numerous group just north of Wolver- 

 hampton. With the exception of some portions at the southern end 



