120 DR. CH. CALLAWAY ON THE rNCONFORMlTIES BETWEEN 



that is, parallel to the overh'ing grits. The strikes in the Wrekin 

 thus agree with those of Lilleshall Hill. 



(c) llie Wroclcwardine Mass. — The rock is mainly rhyolite. There 

 is great variation in the strikes, and they are frequently curved, as 

 we should expect. There is, however, a predominance of what we 

 may call " Longmyndian strikes," such as N. and S., or N.N.E. and 

 ♦S.S.W. Lava-Hows are of course less reliable as indications than 

 clastic beds. At the edge of the area, near Leaton, is a small section 

 of hornstone and volcanic grit, with a high westerly dip. This is 

 the only case in the Wrekin area,, so far as I kno^v, in which clastic 

 rocks have a Longmyndian strike. 



(d) Charlton Bill. — The numerous clear strikes visible in this 

 area are all, with one exception, in clastic beds. The andesitic 

 lava, the conglomerates, grits, hornstones, and argillites have a 

 steady dip to the north, or a little east of north. The strike in the 

 lava as well as several very distinct strikes in grit and conglomerate 

 have been recently discovered, and they agree with my old results. 



(e) The Laiuley. — I have found here but one exposure of sedi- 

 mentary rock with a distinct strike, and that is about E. and W. 



Prof. Blake remarks that some of the rhyolitic-looking rocks in 

 the Church-Stretton district, when microscopically examined, turn 

 out to be slates. I can confirm this statement, though I would 

 rather describe some of these fine-grained compact rocks as argillite, 

 or even hornstone. In the field it is sometimes impossible to dis- 

 tinguish between a sedimentary deposit and a true lava-flow. Prof. 

 Bonuey has examined for me several varieties of compact rock from 

 Caer Caradoc and the hills to the south. He identifies the majority 

 of them as a sort of volcanic mud, one or two as probably igneous, 

 and one or two as doubtful. True lava-flows occur in the middle of 

 Caer Caradoc, in the Hope-Bowdler district, and perhaps elsewhere ; 

 but recent investigations demonstrate that sedimentary material 

 forms a larger proportion of the Uriconian rocks of the Church- 

 Stretton area than we had supposed. This will make the strikes of 

 the region more reliable for our present purpose. Where I have not 

 been able to identify a hard, compact, flinty rock as either igneous 

 or sedimentary, I have found it convenient to employ the vague and, 

 I think, useful term " halleflinta." The strikes in these rocks are 

 usually indicated by a coloured banding or by a platy structure. 



(f ) Caer Caradoc. — The strikes are numerous and clear. Many of 

 them are in hallefiinta, some are in rhyolite, and at the S.W. end there 

 are very good strikes in grit and shaly mudstone. It will be seen 

 from the map that the prevailing strikes are almost at a right angle 

 to the strike of the Longmyndian, which here comes Tjlose up to 

 the Uriconian ; so that on the western side of the hill the discordance 

 of strike may be seen within a couple of hundred yards, the green 

 Longmyndian slates striking N.N.E., while the beds of hallefiinta 

 and grit on the slopes above trend to the N.W. Some of the Uri- 

 conian strikes are seen to form curves, and one of them comes out 

 very clearly. A band of hallefiinta strikes across the ridge in a 

 south-easterly direction, then it bends round to the E., then turns 



