328 Geological Society, 



shows a marked relation to the direction of this line, indicating 

 in all probability a production of schists from the old material in 

 post-Lower Palaeozoic times. 



The western boundary of the Archaean 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 over- 

 fold 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 appears 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 sup- 

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

 Cambrian Series strike up against the Archaean axis being due to 

 faulting. 



The Cambrian is represented by the following series : — 



; Upper Grey Shales. 

 Coal Hill Igneous Band. 

 Lower Grey Shales. 

 Middle Igneous Band. 

 ; Upper Black Shales. 

 Upper White-leaved-Oak Igneous Band. 

 Lower Black Shales. 

 Lower White-leaved-Oak Igneous Baud. 

 2. Hollybusii Sandstone. 

 i. hollybush quartzite and conglomerate. 



Possils are abundant in certain zones of each of the four sub- 

 divisions 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 various Cambrian 

 zones on to the Archaean 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- 

 zone is seen to the west. 



