BASAL CAMBRIAN ROCKS OF SHROPSHIRE. 397 



Such is the eviclence that may be obtained from the Longmynd 

 hills themselves of uii conformity between the two series. It will be 

 seen that the upper series has relations in different spots to 3 distinct 

 members of the lower series No. 3, 4, and 5. It would be still 

 more satisfactory if similar relations were established with Nos. 2 

 and 1. There is little hope of this with regard to No. 2, but the 

 great outlier which lies to the south by Ilorderley shows the grit 

 and No. 1 in contact. On the side of the road from Ilorderley to 

 Marsh Erook, there is a long cliff of dark shale of exactly the same 

 character as No. 1 at Church Stretton, and at Ilorderley we find 

 in it the same calcareous bands. Behind this and above it comes 

 the purple grit as seen at the two ends of the mass. Capping 

 all is a cliff of Caradoc grit, which often by its screes obscures the 

 beds below. This sequence is repeated a second time to the east 

 by means of a fault as represented on the map. Passing south 

 the dark shale is soon lost sight of, and the purple grit swells out 

 into the bulky hill which stretches from Wartle Know! to Aston. 

 The actual present position of those rocks in their relation to 

 each other, is doubtless due to faults (see fig. 3), but the presence 

 of the purple grit at all in this neighbourhood in association with 

 the lowest member of the lower series, is inconsistent with its 

 being conformably situated above No. o. The only question is, are 

 these rocks rightly identified, seeing they are isolated in a faulted 

 outlier ? As to the dark shales, they lie in the continuation of the 

 same band ; and, though on the opposite side of a fault, this fault near 

 Church Stretton is seen to make no dift'erencc in their horizontal 

 position, because the beds are nearly vertical. Moreover there is no 

 other known rock below the Caradoc whicli they can possibly be. 

 As to the purple grit, there is nothing to distinguish it lithologically 

 from the western mass, the nearest exposures in the two areas are 

 less than 1| miles apart, and when last seen it was creeping east- 

 wards. It does not correspond to any other known bed below the 

 Caradoc, and the only alternative is that it is lower even than No. 1. 

 This, I think, would be a very rash hypothesis, resting absolutely on 

 no proof, and rendered extremely improbable by the phenomena of 

 the Caradoc and other volcanic hills, as will be seen in the sequel, 

 llejecting this, then, the proof of unconformity between the purple 

 grit and the underlying series is complete. 



I have gone into full details with regard to this point, because it 

 seems to me to furnish the key to the whole problem of the rela- 

 tions of the various Pre-Ordovician rocks of Shropshire. 



3. Constitution of the ]Ve6'tern Fart of the Lonijmynd Massif. — 

 I must now pass on to the questions raised by the western part 

 of the Longmnyd massif, viz., that which lies between the series 

 already described and the Stiper stones. This western part is con- 

 stituted by three meml)ers,— a lower series of grits and conglomerates, 

 a middle mass of slate, and an upper mass of grit. In the lower 

 mass of grit it has already been noticed tliat the conglomerate does 

 not usually lie at the base, but towards the southern part of its 

 range in the Longmynd it does. So it does also at the extreme 



