214 Br. C. A. Matley — Bunter Pebhle-heds in Midlands. 



those of the Midland Bunter ; but the fact that the Midland Bunter 

 pebbles decrease rapidly in size and number as the beds are followed to 

 the north-west and north-east offers so grave an objection to the theory 

 of a Scottish origin, and on the other hand the palasontological and 

 lithological evidence so strongly supports the view of a southern 

 source for these quartzites, that it seems to me the former theory 

 should definitely give place to the latter. 



There is also another line of lithological evidence which supports 

 the * southern ' theory. Occurring as a characteristic though minor 

 element in the Bunter Conglomerate and as derived pebbles in the 

 Drift are some pebbles of schorl-bearing rocks. Tlie majority are 

 tourmalinized quartzites and grits, some are of schorlaceous breccia, 

 while a few are of schorlaceous granite, the latter being ordinarily too 

 decomposed to be of petrographical value. The presence of such 

 rocks has long been known ; Mr. S. Gr. Perceval collected them from 

 the Drift and Mr. T. H. Waller described them microscopically many 

 years ago, while Professor Bonney did so from the Bunter later ; but 

 their importance as bearing on the general problem of the origin of 

 the Bunter pebble-bed does not seem to have been fully recognized. 

 Although tourmaline-bearing rocks are known in other parts of the 

 British Isles they occur most characteristically and in greatest force 

 in Devon and Cornwall, and the types found as pebbles can be well 

 matched there. To test this fact I selected two pebbles from the 

 Drift near Birmingham, one being a schorl-breccia in which Mr. Gr. 

 Barrow thought he recognized a typical fragment of Cornish ' Killas ' 

 and the other a pebble of exceptionally fresh schorlaceous granite. 

 They are now in the Jermyn Street Collection, and Dr. H. H. Thomas 

 has been good enough to allow me to make use of the following 

 notes of his microscopical examination of thin slices made from 

 them : — 



E. 9553. South of California, near Harborne. Breccia of pale fine-grained 

 rock in dark-grey to black matrix. Schorlaceous breccia. The fragments are 

 mainly of fine-grained quartzose sediments and occasionally of felsite with 

 fluxion-structure. The matrix consists of a mass of the finest acicular 

 tourmaline of blue-green colour. The tourmalinization of the rock as a whole 

 appears to have been accomplished after the brecciation, for the process has 

 affected the larger fragments wherever they contained any aluminous material. 



E . 9554. From a pebble-heap near Kent Cottages, Sheldon, near Birmingham. 

 Schorlaceous granite. The rock is composed of orthoclase, quartz, and 

 tourmaline. The slightly decomposed orthoclase and quartz are intergrown 

 occasionally with an approach to micrographic structure. The tourmaline of 

 the larger crystals is brown, but these crystals invariably have an outer blue 

 layer. The smaller crystals and needles of this mineral are of a blue colour 

 as in luxullianite. The tourmaline occurs alike in the quartz and in the 

 orthoclase. 



Dr. Thomas adds that "It is hard to assign any other source to 

 these pebbles than the West of England, for in that region alone can 

 the types be matched with any degree of closeness ". 



From the above evidence the principal source of the Midland 

 Bunter pebbles seems to me to lie in an area embracing the South- 

 West of England and the North-West corner of France. Until 

 borings yield some positive evidence (which, so far as I know, they 



