Reports and Proceedings — Geological Society of London. 47 



massif, and indicating the presence of a deep and narrow dislocated 

 synclinal fold. In places, the foliation of the schists shovvs a marked 

 relation to the direction of this line, indicating in all probability 

 a production of schists from the old material in post-Lower 

 Paleozoic times. 



The western boundary of the Archtean massif is everywhere 

 a fault, apparently a thrust-plane, but with a small hade. The 

 direction of this plane is in close relation with the axis of the 

 overfold into which the Cambrian rocks are thrown to the west of 

 these hills. 



The western boundary of Chase End Hill is likewise a fault, 

 which is probably a thrust-plane with a tolerably low dip towards 

 the eastern side. The thrust here also appeal's to have been 

 accompanied by a secondary production of schists from the old 

 gneissic series ; and the Cambrian strata are overthrown in the 

 vicinity of the fault. 



There is no evidence for the overlap of the Cambrian Series supposed 

 by Holl, the circumstance that the various zones of the Cambrian 

 Series strike up against the Archsean axis being due to faulting. 



The Cambrian is repi'esented by the following series : — 



4. Grey Shales. 



! Upper Grey Shales. 

 Coal Hill Igneous Band. 

 Lower Grey Shales. 

 Middle Igneous Band. 

 ! Upper Black Shales. 

 Upper White-leaved-Oak Igneous Band. 

 Lower Black Sliales. 

 Lower White-leaved-Oak Igneous Band. 

 2. HoLLYBUSH Sandstone. 



1. HoLLYBUSH QUARTZITE AND CoNGLOMEKATE. 



Fossils are abundant in certain zones of each of the four 

 subdivisions of the series. 



The Grey Shales rest conformably on the Black Shales, but the 

 mutual relations of the remaining subdivisions can be decided only 

 by inference, the junctions being apparently everywhere faults. 

 The junction between the Cambrian and Archaean is likewise a fault. 



All four divisions of the Cambrian Series are invaded by small 

 igneous bosses, laccolites, and intercalated sheets of diabase and 

 andesitic basalt. These igneous rocks do not penetrate the May 

 Hill Series. 



The May Hill Beds seem to rest with apparent conformity upon 

 the Grey Shales, and do not transgress across the vat'ious Cambrian 

 zones on to the Archgean in the manner hitherto supposed, the 

 presumed outliers being small patches faulted into the Cambrian. 



The structure of the district is to be explained on the supposition 

 that we are dealing with the western margin of an old mountain- 

 chain overfolded towards the west ; the eastern portion of this 

 range lies faulted down and buried beneath the Permian and 

 Mesozoic of the Vale of Gloucester. All the characteristics of 

 a folded chain are present, namely, the profound folds, overfolds, 

 thrust-planes, and transverse faults ; and a typical Austonungs-zoue 

 is seen to the west. 



