414 PROF. J. F. BLAKE OJf THE MONIA^ AND 



also a narrow band of hornblende-schist of about the same size 

 as the gneiss on the summit, and near and parallel to it, in con- 

 nection with which may be mentioned a non-foliated diorite on 

 the slope. These patches are so small and so isolated that it is im- 

 ])Ossible to regard them as exposures of bands in a gneissose series, 

 especially as they are surrounded by non-foliated curite : but if the 

 latter be of the nature of a neck, these fragments may very well re- 

 present the underljdng rocks, pieces of which have been torn off and 

 carried up with the eruptive rock. The gneiss is foliated on a large 

 scale, after the manner of the most mylonized gneisses of Anglesey, 

 and the hornblende-schist is practically identical with the foliated 

 diorite of that island. The occurrence of pebbles of gneiss and schist 

 in the Longmynd conglomerates proves that there were large masses of 

 such rocks exposed at the time of their formation ; and the other in- 

 teresting varieties recorded by Dr. Callaway * prove that other rocks 

 which might belong to the same series accompanied them. The horn- 

 blende-schists, however, which would perhaps decay before forming 

 pebbles, have not as yet been recognized. 



These observations therefore tend to show that, as in crossing 

 the Longmynds from west to east we come on ever lower rocks, so 

 if the country still further east could be laid bare, we should find 

 still lower rocks of the same system following in their proper order, 

 the western and all other of the volcanic hills being later outbursts 

 from the uptilted ground and having their own independent bedded 

 pyroclasts. 



§ V. Eelations of the Overlying Formations. 

 1. The Qmirtzite. 



l^eaving on one side the Cambrian conglomerates and grits as 

 already dealt with, the oldest of overlying formation is undoubtedly 

 the quartzite. With regard to this rock, the first point to be noticed 

 is that it never occurs on the west side of the fault. It is, moreover, 

 limited on the south by Cardington Hill, so that it occurs, as it were, 

 only in a bay on the north-east side of the district It does not even 

 mount on to the extreme west of the volcanic hills. It climbs up the 

 sides of Caradoc and occupies the summit of the crest between this and 

 little Caradoc. It laps round the eastern side of the Lawley. It over- 

 passes the Wrekin, it is true, but this hill is not in a geological line 

 with Caradoc, but with Cardington Hill; and, though it reaches Charl- 

 ton and is found as a capping on the slopes of this elevation, it neither 

 reaches the western boundary nor appears at all in the Wrockwardine 

 mass, which has the main fault on its western side. The extreme 

 edge, therefore, of these volcanic hills appears, as far as we can tell, 

 to have formed also its boundary, and they must therefore have been 

 erected into a barrier at the time of its deposition. The occurrence 

 of the Cambrian grit to the east of this boundary, and in fact to the 

 east of the quartzite itself, on Cardington Hill, shows that the barrier 



* Q. J. G. S. vol. xlii. 



