246 MESSES. G. W. LAMPLTJGH AND J. F. WALKER ON [May I903, 



There is no reason to suspect any lateral change in the character 

 of the Gault between the sand-pits and the brickyard ; and indeed 

 the presence of the worn surface on the iron-grit covering the 

 sands : the sharp junction of this bed with the overlying clay : 

 and the entirely-distinct facies of their faunas, render it almost 

 inconceivable that there can be any lateral passage from clay to 

 sand in this neighbourhood. We must therefore conclude that 

 the overlying clay in the sand-pit sections represents Lower 

 Gault, and that the fauna of the calcareous masses is of earlier 

 date. 



In its stratigraphical position and in its relations to the Gault 

 above and to the sands below, the fossiliferous band at Shenley is 

 closely analogous to the Ammonites mammittatus-ked at Folkestone. 

 In the latter case, a fauna considered on questionable grounds 

 to be of Upper Cretaceous age occurs in sands a few feet below the 

 base of the Lower-Gault clays ; its fossils, being mostly in the 

 condition of phosphatized casts, are much less perfectly preserved 

 than those of Shenley Hill. Bat a comparison of the respective 

 faunas, curiously enough, lends little or no support to the correlation. 

 As already stated, the single ammonite found at Shenley Hill is not 

 Ammonites mammillatus ; nor is it the second species of the bed 

 at Folkestone, Amm. Beudanti, var. ligatus x ; and, so far as we 

 know at present, the only species which the beds have in common 

 is Peeten orbicularis, a ubiquitous Cretaceous shell of no value in 

 correlation. 



The fossils of the mammillatus-bed show, indeed, much closer 

 relationship with the Gault-fauna than do the Shenley fossils, which 

 in their faunistic affinities seem to skip over the Gault and claim 

 relationship with the Upper Greensand. On the whole, it appears 

 probable that the Shenley fauna is somewhat older than that of the 

 hiammillatus-bed, and was separated by a longer time-interval from 

 the beginning of Gault-conditions. Subsequent remarks touching 

 the desirability of retaining the Shenley bed in the Lower Cretaceous 

 system will apply, however, with almost equal force to the case of 

 the zone of Ammonites mammillatus. 



As to the relationship of the Shenley fauna with other fossiliferous 

 horizons in the Lower Greensand, to which reference has been 

 already made, it will be observed from the lists of fossils (pp. 262-63) 

 that the bed has yielded a few species which occur also in the Faring- 

 don 'Sponge-Gravels,' or atBrickhill, or Upware, or in the 'Bargate 

 Beds ' of Surrey. But the general assemblage at all these places, 

 especially of the prevalent brachiopods, is entirely different from 

 that at Shenley ; and the absence of some of the commonest and 

 most characteristic forms, along with the presence in abundance of 

 others which are unknown at these places, make the difference of 

 the fauna much more striking when the respective collections are 

 examined than is apparent from the mere inspection of the fossil- 

 lists. The laniellibranchs show a somewhat closer affinity to the 



1 ' The Cretaceous Eocks of Britain ' vol. i, Mem. Geol. Surv. (1900) p. 443. 



