386 PROF. J. F. BLAKE OX THE MOXTAN AXD 



21. On the Moniax and Basal Cambrian Hocks 0/ Shropshire. By- 

 Prof. J. F. Blake, M.A., F.G.S. (Head 3Iarch 12, 1890.) 



[Plate XVL] 

 Contents. 

 § I. Introduction. 



§ II. Stratigraphy of the Loxgmvnd Hills. 



1. General. 



2. The Junction-line between the two Series (Lower and Upper) 



in the Longmynd. 



3. Constitution of the Western Part of the Longmynd Massif. 



4. The Western Boundary of the Longmynd Massif, with the sup- 



posed Archaean Masses. 



5. Summary of the Stratigraphy of the Longmynd. 



§ III. Stratigraphy op the Volcanic Hills. 



§IV. Possible more Ancient Eocks in the District. 



§ V. Relations op the Oyeklving Formations. 



1. The Quart zite. 



2, The Succeeding Foi-matious. 



§VI. General Conclusions. 



^ I. Intr 



ODUCTION. 



Ix my memoir " On the Monian system " as developed in Anglesey *, 

 I suggested that the Longmynd rocks might belong to the Upper 

 Monian, on account of their general similarity to those of Bray Head, 

 and that the Uriconian rocks of Dr. Callaway might be Middle 

 Monian, because they were at once Precambrian and Volcanic As 

 these suggestions, which would be of some importance if true, were 

 matters of conjecture only, I have taken the first opportunity to 

 examine the district with care in order to arrive at a definite con- 

 clusion. 



At the time of my writing, it was the universal opinion that the 

 Longmynd series were essentially, even if not typically Cambrian ; 

 but about the same date Dr. Callaway was suggesting to the local 

 geologists of Shropshire that in view of the break that existed be- 

 tween his " Hollybush Sandstone,'' which he regarded as Menevian, 

 and the Longmynd series, it was doubtful if the latter were really 

 Cambrian, and he proposed that till this was decided, they should be 

 called Longmyndian t. The same argument was more strongly en- 

 forced last year J by Prof. Lap worth, who writes, " the presence of 



* Quart. Journ. Geol. Soc. vol. xHv. 

 t Trans. Shrops. Archreol. Soc. 1887. 

 X GeohMag., .Nov. 1888. 



