68 ME. G. W. LAMPLrGH O^ THE JUIfCTIOX OF [yoI. Ixxviii, 



of a greater thickness o£ clay. The fossils of the nodules include 

 man}' that are characteristic of the lower part of the Upper Grault ; 

 therefore, as at Folkestone, it is a convenient ' Junction-bed ' for 

 the subdivisions. 



It is particularly to be noted that no extraneous pebbles have 

 been found in this nodule-bed. Indeed, its clay-matrix is not even 

 gritty; and the condition and position of the ammonite-casts 

 mentioned in the earlier part of this paper (footnote, p. 9), 

 together -with the very variable size and shape of the nodules, 

 afford further proof that the sea-currents at this stage were too 

 weak to shift any heav}^ material. 



The absence of pebbly matter and of any fragments of iron-grit 

 marks the sharp difference between this bed and the Basement-bed of 

 the Lower Grault. In no part of the district, nor indeed elsewhere 

 in England, so far as I am aware, has any bed resembling the 

 irongrit-breccia been found intercalated between the Upper and 

 the Lower Grault. 



The higher part of the Upper Gault requires no discussion in 

 this paper. So far as seen, it is quite different in aspect and fossils 

 from the cla^-s with which I have dealt (see p. 37). 



V. DlSCUSSIOlS^ OE THE ' OyEETTJEN ' HYPOTHESIS. 



I niay now, before concluding, enter into a pai'ticular consider- 

 ation of the points of issue raised b}^ Dr. Kitchin & Mr. Pringle, 

 although most of these have, I think, been incidentally met and 

 controverted b}" the foregoing descriptions. The supposition that 

 the Gault, limestone, and glauconitic sand at Shenley Hill have been 

 inverted by Glacial action is based mainly upon a palseontological 

 argument, to explain the presence of some fossils in the limestone, 

 that were not previously known to occur below the English Gault. 

 The anomalous character of the fossil-assemblage in this respect 

 was duly discussed and, I think, adequately explained in our 

 previous paper ; but our explanation has been set aside. In support 

 of their palseontological argument, Dr. Kitchin & Mr. Pringle 

 have brought forward some stratigraphical considerations, which I 

 will deal with first. 



The stratigraphical argument. — Some fundamental 

 points telling strongly against the inversion -theory were stated in 

 my letter to the Geological Magazine (May 1920, pp. 234-37 )^ 

 close upon the publication of the hypothesis. The gist of these 

 may be re-stated in brief as follows : — ■ 



(1) The absence of any rock resembling the peculiar Shenley limestone, 

 either in composition or in fossils, from any part of the outcrop above the 

 Gault in the Chiltern escarpment, and the entirely different character of the 

 known beds at this horizon. 



(2) The unweathered condition of the thin cakes of limestone and of the 

 wedg-e of loose glauconitic sand, which are supposed to have lain at the 

 surface before being overturned. 



