AUSTEN — EXTENSION OF THE COAL-MEASURES. 71 



Mr. Prestwich. which confirmed the view I had taken in a most 

 remarkable manner. The boring at Kentish Town, after having 

 been carried through the whole thickness of the Chalk and the 

 Gault, passed to beds of red marl and sandstone, to the exclusion of 

 any beds having the least resemblance to any portion of the Lower 

 Greensand. Since this paper was originally read, the details of the 

 Kentish Town well have been communicated to the Society*. The 

 presence of a coarse conglomerate bed subordinate to the Gault, 

 is a feature wholly at variance with the composition of that deposit 

 round the whole circuit of the Wealden denudation ; but that it be- 

 longs to the Gault is probable from the presence of a Belemnite very 

 like Belemnites Listen. Considering this conglomerate with refer- 

 ence to the size and mineral character of the rocks it contains, it is a 

 good representative of the calcareous portions of the Tourtia of the 

 Pas de Calais, and of Belgium, and its presence on our side of the 

 Channel shows that the peculiar physical line which, as was shown 

 long since by M. d'Archiac, both defined and caused that local 

 accumulation was extended across into our areaf . 



The Tourtia conglomerate belongs to the northern slope of the old 

 Palaeozoic axis of Artois, and in this way the Kentish Town boring 

 directly solves one of the most important points of this inquiry. 

 Taking the narrow dimensions of the axis of Artois, when compared 

 with the great expanse of the Wealden, with its high anticlinals, it 

 might have been urged that some of these marked the course of the 

 old line of disturbance, and hence the field over which the coal-band 

 might be expected to occur would have been materially enlarged. 

 We can now feel certain that the Kentish Town conglomerate has 

 reference to the same northern slope ; that the axis, therefore, passes 

 beneath the range of the North Downs ; and that the depression of 

 the Thames Valley represents, and is physically a continuation of, 

 that which, extending from Valenciennes by Douai, Bethune, The- 

 rouanne, and thence to Calais, .includes the great coal-trough of those 

 countries. 



Whatever may have been the original range of the Oolitic group 

 over the area now covered by the Wealden and Cretaceous formations 

 of the S.E. of England, there is evidence that it has been reduced by 

 the abrading action of the Lower Greensand sea along its coast-line. 

 The shingle-beds of the Lower Greensand of Surrey and Kent con- 

 tain, in addition to the materials already alluded to, a considerable 

 number of extraneous fossils, such as the bones and teeth of Oolitic 

 Saurians, Ammonites Lamherti and A. crenatus of the Oxford Clay, 

 in great abundance, together with Terebratula fimbria and Rhyn- 

 chonella oolitica. 



Beds of this Oolitic age are brought up, as we have seen, against 

 the S. slope of the French axis, and hence we see that the coast-line 

 acted on during the Lower Greensand accumulations consisted partly 

 of oolitic and partly of older rocks, and that for a given breadth the 



* Vide supra, p. 6. 



t For the composition of the conglomerate-band passed through by the Kentish 

 Town well, I beg to refer to Mr. Prestwich's paper. 



