part 1] OATJLT AND LOWEE GREENSAND NEAR LEIGHTOjS'. 71 



consolidated clay' (K.P., p. 58) may in one sense be allowed, but 

 not in the sense implied by the authors, who consider that the 

 structure is original and indicative of a definite horizon in the 

 Gault. In such shallow sections as those in which the ' race ' and 

 the brecciated structure are seen, one could hardly expect to find 

 soft calcareous clays of the Gault type in their original condition, 

 particularly on sloping ground. 



The interpretation of the thin continuous band of Basement beds 

 around Shenley as being 'a remarkable collocation of heterochronous 

 elements' (K.P., p. 12), composed in part of post-Glacial iron-grit, 

 in part of Glacial gravel, in part of Cenomanian limestone, in part 

 of Upper Greensand, and in part of an Upper Gault Basement bed 

 containing derivative Lower Greensand fossils, is so entirely 

 dependent upon the palseontological argument that it requires 

 further consideration only from the palseontological standpoint, 

 which I shall now attempt. 



The palseontological argument. — As bearing on the 

 general aspect of the fossil-evidence, we may recall that this is at 

 least the third time in English geology that fossiliferous beds 

 occurring below the Gault have been held, on palseontological 

 grounds, to be newer than the Gault. First, the Faringdon Sponge- 

 Gravels, notwithstanding previous opinion, now accepted, were 

 supposed by T. Davidson, i on the evidence of their brachiopoda, to 

 be possibly of Upper Greensand age; and by D. Sharpe,^ because 

 of their polyzoa, to be newer even than the English Chalk, and 

 probably 'Danian.' Particular stress was laid by both authors on 

 comparisons with the Tourtias of the Continent; but, as Caleb 

 Evans 2 pointed out, the argument might be legitimately reversed 

 by questioning the reputed age of the Tourtias — themselves of 

 uncertain antecedents. 



Again, some 30 3^ears later, the presence of the Gault in part of 

 West Norfolk was challenged by C. Reid & G. Sharman,^ who 

 argued that the calcareous clay in question was the Chalk Marl, 

 mainly on the ground that — 



' not a single characteristic Gault form occurred, but that there were 

 several species which haye not been recorded from below the Lower Chalk,' — 



the unquestionable Gault species in a phospha tic -nodule bed at the 

 base of the clay being all regarded as ' derivative.' The challenge 

 was answered effectively by A. J. Jukes-Browne & W. Hill,^ who 



1 ' Monogr. Brit. Cret. Brachiopoda ' pt. ii, p. 3, Pal. Soc. 1852. 



^ ' On the Ag-e of the Fossiliferous Sands & Grravels of Faringdon & its 

 Neighbourhood' Q. J. G. S. vol. x (1854) pp. 176-98. 



3 ' Sketch of the Geology of Fa.rringdon ' Geol. & Nat. Hist. Eepertory, 

 containing Proc. Geol. Assoc. No. 16, Aug. 1866, pp. 33-40. 



•* ' On the so-called " Gault " of West Dereham, in Norfolk ' Geol. Mag. 

 1886, pp. 55-59. 



5 ' Note on the Gault & Chalk Marl of West Norfolk ' Geol. Mag. 1886, 

 pp. 72-74 ; and ' On the Lower Part of the Upper Cretaceous Series in West 

 Suffolk & Norfolk ' Q. J. G. S. vol. xliii(1887) pp. 547-49 & 571-74. 



