80 PBOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 20, 



Formations present. Formations absent. 



feet. feet. 



Fbrest Marble (greatest thickness) 150 



Great Oolite (Lower Zone) 100 



Fuller's Earth 200 



Inferior Oolite 270 



Sands 150 



Upper Lias Clay 400 



Marlstone? 240 



Lower Keuper Sandstone 450 



Bunter Sandstone 2150 



Oxford Clay 600 



Cornbrash 5 



Great Oolite (Upper Zone) 200 



Lower Lias 200 ? 



Red Marl (Keuper) 200? 



Lower Permian Beds ? 



Coal-measures x ? 



§ 7. General Conclusions. — From the foregoing considerations the 

 following conclusions may be drawn : — 



1st. That during the deposition of the Upper Palaeozoic and 

 Lower Mesozoic Rocks an extensive tract of land existed to the 

 north-west of the British Isles, which afforded the materials of 

 which these rocks are composed ; and it is probable that this region 

 embraced the western isles and coast of Scotland. 



2nd. That the Lower Permian Rocks were deposited in a channel, 

 of which we can trace approximately the borders to the west and 

 north-east ; and that this group attains its maximum development 

 along a band of country stretching west and east, from the southern 

 borders of Salop, across Staffordshire to Warwickshire. 



3rd. That at the close of the Permian Period there ensued con- 

 siderable changes in the distribution of land and sea, involving a 

 large increase in the latter. That a highway was opened between 

 North Wales and Westmoreland, along which the sediment for the 

 formation of the Lower Secondary rocks was transported by an 

 oceanic current and spread over the plains of England, filling up 

 old Palaeozoic valleys. 



4th. That all the Lower Secondary formations decrease in thick- 

 ness, and actually die out towards the south-east ; that this atte- 

 nuation is due to the increase of distance from the sources of supply, 

 and the consequent failure of sedimentary materials which have 

 come from land occupying the region of the North Atlantic. 



5th. That there probably exists a tract of Coal-measures stretch- 

 ing from the southern borders of the Staffordshire and Warwick- 

 shire Coal-fields towards the Thames Valley, as previously surmised 

 by Mr. Godwin-Austen, but that there is reason to fear that the 

 whole formation becomes debased and less likely to contain valuable 

 beds of coal. 



6. That the depth to the Coal-measures under parts of Oxford- 

 shire and Northamptonshire cannot, in consequence of the thinning- 

 out of the Lower Secondary Rocks (Inferior Oolite, Lias, and Trias), 

 be considered as beyond the reach of mining enterprise ; but that the 

 thickness of the interposed Permian rocks and the economical value 

 of the coal-beds are points of uncertainty, which are likely to be 

 solved only by actual experiment. 



