404 PROF. J. E. BLAKE OS THE MONIAN AND 



copper vein in the neighbourhood, as the fragments are all tinged 

 with the green salts of that metal. But the rock is unquestionable ; 

 it is the ordinary follower of the grits throughout the district. 

 This, then, is not Arch^an. 



At the southern base of this hill there is a transverse fault 

 bringing up the conglomerate alongside of the slate. This con- 

 glomerate is followed to the west in the south end of Chittol Wood 

 by a mass of compact felsite, very like that of the Knolls E-idge, 

 whose relative position it occupies, and whose interpretation it will 

 therefore follow. 



On the western banks of the West Onny river, by the side of 

 Linley Drive, we have a series of very instructive sections. All the 

 rocks have a dip of about GO to the W. by I^i., and the river crosses 

 them successively. They consist of a series of alternations of 

 rock, some of which exactly resemble the purple grits, and others 

 the compact Chittol slates, and others are of intermediate character ; 

 we could not desire a better illustration of the passage upwards 

 from the grits into the slates. But these beds, though quite con- 

 formable in their strike with the grits of Linley Hill itself, are so 

 situated that if continued either way they would run into the masses 

 of felsite exposed in the neighbourhood. They would equally run 

 into the associated greenstones, and we have no reason in either 

 case to assume these igneous rocks to be anything than intrusive. 

 Whatever, therefore, the exposures of acid rocks at Knolls Wood 

 and Oldmoor AVood may be, there is no reason to call them Archaean, 

 unless we are prepared to maintain that every acid rock of volcanic 

 origin, or composed of volcanic fragments, is ijjso facto, Archaean. 

 The supposed ridge of Pre-Cambrian rocks in this district is there- 

 fore non-existent ; the whole is of Lower-Cambrian age. 



5. Summary of the Stratir/raphy of the Loncjmynd. — The results 

 obtained up to this point may be summarized as follows : — There 

 are two series of rocks in the Longmynd ; the lower series is divi- 

 sible into five portions, which may be traced across the country and 

 into the outliers. The upper series lies on this unconformably, and 

 is seen in various parts in relation with four out of the five sub- 

 divisions of the lower series. It consists of three main members, 

 which are reduced to one in the north by the dying-out of the 

 middle one. There is no sign of a synclinal in the whole range, 

 but the normal dips get smaller to the west. The rocks succeeding 

 this tripartite series are pale hard slates, whose normal succession 

 may be seen in the south, but elsewhere may possibly be obscured 

 by a fault, near which several masses of acid igneous rock have 

 intruded transversely. The pebbles in the conglomerate may pos- 

 sibly have been partly derived from some portions of the older 

 series, but it certainly contains pebbles not only of quartzite imseen 

 in the neighbourhood, but of acid volcanic rocks also. 



Now Dr. Callaway has irresistibly argued from finding sucli 

 acid igneous rocks in the neighbouring hills of the Wrekin, Caer 

 Caradoc, and others, that we must regard the conglomerates as 

 derived from them, and therefore as of later date than they, pro- 

 vided the stratigraphy permits it. 



