ON THE ARCHJ5AN ROCKS OF GREAT BRITAIN. 535 



granitoid rock. This continues for aboat a quarter of a mile, and is 

 then abruptly succeeded by rhyolite (the commencement of the main 

 massif), the junction being probably a faulted one. It is possible that the 

 junction on the northern side may also be a fault, but to myself the 

 appearances appear much more favourable to the idea that the rhyolite 

 has broken through the granitoid rock. The latter consists of quartz, 

 felspar (orthoclase, oligoclase ? and probably mierocline), with some iron 

 peroxide and a small quantity of a chloritic. mineral. It is extremely 

 difficult to say whether it be a true granite or a granitoid gneiss (grani- 

 toidite), but it seems impossible to doubt that it is a much more ancient 

 rock than the rhyolite. At Primrose Hill, at the southern end of the 

 range, the rhyolite again gives place to ' granitoidite ' of the Ercal Hill 

 type, with gneiss of Malvernian type and a little diorite. 



Evidences of Geological Age. — Even if we consider the 'granitoidite' 

 igneous, it must be older than the rhyolitic group, and we can hardly 

 hesitate to recognise in some of the Primrose Hill rocks a reappearance 

 of the ancient Malvernian gneisses. At any rate, the rhyolitic group is 

 much earlier instead of later than the Caradoe, for Dr. Callaway has 

 shown that the quartzite which flanks the Wrekin is considerably older 

 than the Hollybush sandstone 1 (Lingula Flag), and it contains in parts 

 fragments of the rhyolitic rocks of the Wrekin. Hence the latter must, 

 at the latest, be Cambrian, or even older. 



The rhyolitic group reappears to the north-west of the Wrekin, at a 

 distance of rather more than a mile, in the neighbourhood of the village 

 of Wrockwardine ; and near the southern end, at Lea Rock, there is a fine 

 mass of the ancient ' pitchstone,' exhibiting in parts beautiful perlitic 

 and spkerulitic structures, which have been described and depicted by 

 Mr. Allport. 



At Charlton Hill, along the same line to the south-west, there are 

 argillites, tufls, and felstones, some of the latter being of the Wrekin type, 

 but one is porphyritic and apparently rather less acid, together with a very 

 interesting conglomerate, containing well rounded fragments of quartz, 

 felspar, gneiss, and various schists, indicating that the materials were 

 derived from a series of metamorphic rocks. 



Lilleshall Hill, a low ridge, about five miles to the north-east of the 

 Wrekin, consists of hard argillites, ashy slates, and rhyolitic agglome- 

 rates, with a small coulee (?) of rhyolite, the latter closely resembling 

 the same rock in the Wrekin. Average dip 40° to NNW. 



There are exposures of rocks resembling the above described volcanic 

 group in the district between the Wrekin and Caer Caradoe, at the latter 

 locality, at Hazier Hill, Raglett Hill, and near Hope Bowdler, and some 

 more west of the Longmynds, but as they are inferior in interest to those 

 already described it may suffice to mention them. 2 



(c.) The Lickey Hills. — This range forms the eastern boundary of 

 the Severn valley, lying rather more than twenty miles north-east from the 

 Worcester Beacon (the culminating summit of the Malvern chain) and 

 about the same distance south-east of the Wrekin. The principal rock is 

 a quartzite bearing considerable resemblance to that which flanks the 

 Wrekin, the constituents of which have probably been derived from 

 granitoid rocks. Formerly this rock was regarded as altered Llandovery 



1 Q. J. (!. S., vol. xxxiv. p. 701. 



'' Sfu Callaway, loc. tit,, and vol. xxxviii. p. 11 'J. 



