BASAL CAMBRIAN KOCKS OF SHKOPSHIKE. 405 



If the LoDf^mynd conglomerates are Cambrian, the volcanic hills 

 themselves must be in some sense Pre-Cambrian, so must they be 

 also if the conglomerates are Pre-Cambrian. To use Dr. Callaway's 

 names, so long as the Longmynd series was undivided, it was certain 

 that the " Longmyndian " must be younger than the " Uriconian." 

 But now that I have shown that there are two unconformable 

 series, this argument only applies to the upper series which contains 

 the conglomerates ; and the relation of the older series to the 

 Uriconian is left entirely undecided, and must, if possible, be deter- 

 mined by details of stratigraphy. To this I now apply myself. 



§ III. Stratigraphy of the Volcanic Hills. 



It is not my intention to go into all the details of these hills ; 

 they have been already described by Dr. Callaway, and are now 

 receiving the attention of Prof. Lapworth. To him the many points 

 of general interest in their structure may be left, and those only 

 attended to which have some bearing on the age of the rocks. The 

 place to commence our examination of these hills in their relation 

 to the Longmynds is obviously where the two come closest together 

 in the neighbourhood of Church Stretton. 



The first question to deal with has relation to the fault that is 

 there drawn between the two. In the south of this district, from 

 Aston-on-Clun by Hopesay, Hordeley, and Marsh Brook, this fault 

 may be traced without a shadow of doubt. It has here a re- 

 markably straight course with only a general curvature to the east. 

 Leaving it now for the moment from the southern end of Bagleth to 

 that of Caer Caradoc, we find the western boundary of the latter a 

 remarkably straight line, as is that of the Lawley ; and the suc- 

 cession of beds on the west proves this to be a continuation of the 

 fault. Thence it is traced on the Survey Map as far as the Severn, 

 near Cound Villa, and if still continued it v/ould form the approxi- 

 mate western boundary of the Wrockwardine mass. It is therefore 

 a very continuous fault. But it does not appear that its throw is 

 very great ; Professor Bamsay estimates it at 2000 feet ; but, con- 

 sidering the overlap of the Llandovery which reaches the Longmynd 

 elopes, and must be thinning out, this would appear to be a maximum. 

 If now we continue the line of this fault across the interval 

 omitted, ^. e. from Ragleth to Caer Caradoc, we must either assume 

 that it zigzags about just here in an unaccountable manner, and as 

 it does nowhere else, or we must leave some of the l^ongmynd 

 shales on the eastern side of it, as is done by the Survey. With the 

 high dip of these dark shales to the west, an upthrow of 2000 feet 

 on the east would not cause a loss of more than 200 feet on the 

 surface, so that we should still be probably in the dark shales on 

 the eastern side of the fault. Now all the slopes of Bagleth are in 

 the dark shales. They are seen very near the line of fault at the 

 crossing of Watling Street and the Church-Stretton road, from 

 which spot .there is an almost continuous section exposed up two 



Q. J. G. S. No. 183. 2 g 



