"Vol. 56.] BUNTER PEBBLE-BED9 OF THE MIDLANDS. 295 



occupying about one third of the space. These fragments, with 

 crossed nicols, exhibit a chalcedonic structure, and I think that they 

 represent a silicified pitchstone. In these tourmaliniferous rocks I 

 have occasionally come across a few granules, often associated, of 

 a honey-brown colour, and a rather high refractive index, which 

 may possibly be cassiterite. 



One breccia remains (Baland's Pool Pit) which microscopically 

 resembles a fairly well-preserved, reddish gneissoid granite. Micro- 

 scopic examination shows it to be a coarsely crystalline, almost binary 

 granite (some microcline), pressure-modified, and recemented by 

 mosaic quartz, with some interspersed opacite or ferrite, associated 

 occasionally with a prismatic, colourless, microlithic mineral, appa- 

 rently monoclinic, and possibly a very little epidote. The rock 

 might be derived from an Archaaan mass. Both granitoid rocks and 

 crystalline schists do occur in the Bunter Conglomerate, but are rare 

 and generally very rotten. This one has probably been preserved 

 by the infiltration of silica. 



III. Transport of the Pebbles. 



Such being the evidence which I have been able to collect as to 

 the materials of the Bunter Pebble-beds in the Midlands, we have 

 next to consider by what agency they have been brought thither and 

 from what source or sources they have most probably been derived. 



The former of these questions need not detain us long. They 

 cannot, as I have more than once pointed out, be lacustrine deposits ; 

 hence they must be either marine or fluviatile. Mr. Mellard B-eade 

 maintains the former view, 1 and no doubt this would avoid some 

 difficulties, but these beds, as has been shown by myself and others, 2 

 are very unlike marine deposits, differing most of all in being at 

 once widespread and thick, and so not resembling any shingle-beds 

 of which I have knowledge. Hence they must be fluviatile; 

 but this admission, which now seems general, involves certain con- 

 sequences, to which I shall refer presently, since they seem to have 

 been frequently overlooked. 



In discussing the second question, the source of the pebbles, I must 

 be understood to refer to the more numerous and distinctive rocks, 

 for the Midland Bunter contains so great a variety that I suspect 

 them to represent a very wide drainage-area. As a large river 

 receives many tributaries, it may very well happen that, while the 

 bulk have come from one quarter, say from the north, others have 

 been contributed by districts lying more nearly east and west. In 

 this particular case the south only would seem to be improbable, if 

 not excluded, as a direction. 



Any locality which claims to be the source of these pebbles must 

 satisfy two conditions : (1) it must have an adequate supply of the 

 right kinds of rocks, and (2) be capable of feeding rivers large 



1 Geol. Mag. 1889, p. 549 ; ibid. 1890, pp. 155 & 260. 

 a Rep. Brit. Assoc. 1886 (Birmingham) etc. 



