64 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 20, 



Thames Valley, as the focus of my remarks lies in the district of 

 Oxfordshire, with the geological structure of which our learned 

 President is so intimately acquainted. 



My way has been, to a certain extent, prepared by the elaborate 

 Essay " On the possible Extension of the Coal-measures beneath the 

 South-eastern Part of England, " by Mr. Godwin-Austen, commu- 

 nicated to this Society*. This essay and the researches of Mr. Prest- 

 wich have excited much interest regarding the rocks which underlie 

 the Cretaceous and Oolitic formations. It is with the object of 

 throwing some further light on this important subject that the 

 following observations and deductions have been drawn up. 



It is almost unnecessary to reiterate here what is now so fully 

 understood, from the researches of D'Archiac, Pozet, Prestwich, and 

 especially of Godwin- Austen, that along the line of the Franco- 

 Belgian Coal-field the Cretaceous and Nummulitic rocks repose on 

 the highly inclined edges of the Palaeozoic Eocks without the inter- 

 vention of those of the Lower Secondary periods. Iu the district of 

 the Bas-Boulonnais similar phaenomena are observable ; but we learn 

 from the memoir of M. Pozet that strata referred to the Great Oolite 

 abut against the northern flank of the Palaeozoic range and rest on 

 a bed of Carboniferous Pocks f. 



Adopting the theory of Mr. Austen regarding the extension of the 

 Palaeozoic axis of elevation under the Thames Valley, I do not, how- 

 ever, consider that the entire absence of all the intervening formations 

 between the Great Oolite and the Coal-measures is to be attributed 

 altogether to the presence of this old coast-line, but to other causes 

 to be hereafter stated. I shall endeavour to show that all these 

 formations decrease in thickness, as they approach the south-east of 

 England, from the failure of sediment, in the manner of deposits 

 forming at the mouths of large rivers. 



I also propose to inquire whether the Uppermost Palaeozoic rocks, 

 namely the Coal-measures and Permian deposits, are regulated in 

 their distribution upon a similar physical plan ; or whether they may 

 not have a much wider range, and extend into districts where many 

 of the more recent formations cease. 



Lastly, whether there are not reasons for concluding that under 

 certain districts of Oxford and Northampton the Coal-measures lie 

 at available depths below the surface, owing to the thinning away 

 of the Lower Secondary rocks. 



§ 2. Distribution of the Lower Permian Beds of Central England. 

 — TJpon comparing the Lower Secondary with the Uppermost Pa- 

 laeozoic formations, we discover a very marked difference in their 

 distributions. We find the Bunter-Schiefer and Zechstein appearing 

 only in the north-eastern districts of England, and the Pothe-todte- 

 liegende confined principally to the central counties and Salop ; while 

 the Trias is most fully developed towards the north-west. 



Eef erring to the works of Sedgwick %, Murchison§, Eamsay||, 



* Quart. Journ. Geol. Soc. vol. xi. p. 533. 



f Rozet. ' Description Geognostique du Bassin du Bas-Boulonnais.' 

 \ Trans. Geol. Soc. 2nd Series, vol. iii. § ' Siluria,' new edit. 



|| Quart. Journ. Geol. Soc. vol. xi. p. 185. 



