Yoi. 68.] CAEBONIFEROTJS LIMESTONE AT UPPER VOBSTEE. 67 



Vobster Old Quarry. (PL IV fig. 2, PI. V, & text-fig. p 68.) 



West of the tunnel, the quarr3'-face gives a good section of D^ 

 limestones overlain by grits and shales. This section, the eastern 

 part of which is seen in PI. lY, fig. 2, extends from the western 

 extremity of the quarry as far as a prominent bluft' about 50 yards 

 west of the tramway {efg on the map, PI. II). Throughout the 

 section the beds have a general northerly dip ; but, in consequence 

 of synclinal folding, the greatest thickness of Grit-&-Shale beds 

 is found near the middle of the section, while at the western end 

 a mere capping of grit-&-shale debris overlies the limestone. 



Immediately overlying the Carboniferous Limestone beds, which 

 are hard grey limestones for the most part, are the Grit-&-Shale 

 beds. 



These latter, examined at the point where they occupy a maximum 

 depth of a little more than 20 feet of the quarry-face, were found to- 

 comprise the following beds, in descending order i : — 



(c) Compact pink and yellowish quartzites : in part very fine-grained ; 

 in part of coarser grain, and speckled with rusty ferruginous spots, [And 

 debris of same to top of section.] 



{h) Fine-grained, greenish, argillaceous sandstones. 



(a) Blue-black micaceous shales, much ironshot, and containing 

 lenticles of fine-grained sandstone. 



The combined thickness of (a) and (Jj) is about 8 feet. 



This junction of Carboniferous Limestone with Grit-&-Shale 

 beds is undoubtedly a faulted one ; and, although the section is 

 much overgrown, it can be seen that the stratification in the two 

 formations is not precisely concordant. In the bluff at the eastern 

 end of the section the limestone-beds are distorted and broken. 



East of this bluff (^), debris now obscures the rocks as far as the 

 tunnel and for some distance beyond it. Thanks to Mr. Winwood's. 

 description " of the tunnel-section, however, we know that in the 

 mouth of the tunnel the Carboniferous Limestone appears to dip 

 steeply southwards, and is underlain on the north by shales and 

 quartzites which have nearly the same angle of dip. Here, then, 

 the succession of limestones, shales, and quartzites already seen in 

 the quarry-face to the west is inverted, and the fault-plane between 

 the Carboniferous Limestone and the Grit-&-Shale beds hades 

 southwards instead of northwards. Our section (PI. II) crosses the 

 junction at this point. 



We must conclude that the beds of Carboniferous Limestone, 

 where they are inclined southwards, as in the tunnel itself and at 

 various points in Yobster Old Quarry on the east, are inverted. 

 The evidence leading to this conclusion is as follows. 



About 35 yards east of the tunnel the bare surfaces of some 

 limestone-beds, steeply inclined southwards, form the lower part 

 of the quarry-face {h on the map, PI. II, and in the text-figure^ 



1 This section was described by the Eev. H. H. Winwood, 1885, p. 30. 



2 Winwood, 1893. 



p2 



