1859. J HULL THINNING-OUT OF THE SECONDARY EOCKS. 79 



field ; and a still more remarkable one occurs in South Staffordshire, 

 where the " Main Coal" of Dudley, 10 yards thick, becomes split up 

 into several seams at the northern part of the coal-field, and se- 

 parated by sandstones, shales, and clays, altogether attaining a 

 thickness of 300 feet. This fact has been demonstrated by Mr. 

 Jukes*, who remarks upon the great persistency of the coal-beds as 

 compared with the inorganic materials. The Tordale series of 

 Lancashire and North Staffordshire are enormously developed in 

 comparison with their equivalents in Leicestershire and "Warwick- 

 shire. With all these facts in view, it is much to be feared that 

 the Carboniferous Series generally becomes greatly reduced, and 

 probably much less productive of coal, under the districts of 

 Oxfordshire and Northamptonshire. 



Mr. Sorbyt has also carried on a series of investigations on the 

 currents of these ancient seas, as indicated by the various phaeno- 

 mena of stratification. It is probable that, when completed, these 

 will lead to results of the highest interest in throwing light upon 

 the physical geography of past times. In the meantime Mr. Sorby 

 appears to have arrived at the conclusion, that the drifting of sedi- 

 ment has been from the N.W. in the case of the Carboniferous 

 group ; while tidal currents ebbed and flowed in N.E. and S.W. 

 directions throughout parts of the Permian and Oolitic periods J. 

 All these phenomena point to the existence of a continent, or at 

 least of an extensive tract of land, throughout the Carboniferous, 

 Permian, and Lower Secondary Periods in the region now occupied 

 by the North Atlantic Ocean. 



Accepting, then, the conclusions of Mr. Godwin- Austen, that a 

 band of Coal-measures stretches along the Thames Valley, thrown 

 off on the north side of the Old Palaeozoic Axis, it is not improbable 

 that the formation extends, with perhaps occasional interruptions, 

 into the central counties; but I have already hinted at the probability 

 that, as a coal-producing set of rocks, it has become deteriorated in 

 its extension southwards (page 71). 



With regard to the formations which may be inferred to he above 

 the Coal-measures in Oxfordshire and Northamptonshire, it is pro- 

 bable we should find the following ascending series : — 



1st. The Lower Permian codas, of considerable depth northward, 

 but diminishing in thickness tow, nils the escarpmen.1 of the Chalk. 



2nd. Above tin- lVnni;m heds, we should find no Hunter Sand- 

 stone, but. only the Keuper Maris, greatly diminished in thickness. 



3rd. Next the Lower Lias, also greatly reduced and thinning 

 away towards the Chalk-escarpment. If the Marlstone and I'jipei- 

 Lias were found to exist, it would only be as mere traces, and these 



would be immediately superimposed by the Upper Z <»r •• White 



limestones" of the Qreai Oolite, 



A vertical section under Oxford would probably present the fol- 

 lowing descending series: — 



* South Staffordshire Coal-field: Ifem QeoL Survey 



t Sec Papers in (lie I'Min. Phil. Journal. New Series 



: Bee ' Sutuifl ' 3rd i dil Lpp ndix. 



