70 MB. G. W. LAMPLTJGH ON" THE JTJN^CTION OF [vol. Ixxviii, 



accompanied by arguments based on the lithology, preluded by the 

 general statement — 



' It is a matter of surprise to us that this clay [in Harris's pit] has even 

 been mistaken for Lower Gault ' (K.P., p. 13). 



This, however, merely expresses a personal impression, which is 

 not likely to be shared by anyone who examines all the exposures of 

 the Gault in the district, and notes the very different aspect of the 

 Upper Grault in the undisputed sections farther south (see p. 37). 

 The ' true Lower Gavilt of the district,' with which the loAver clay 

 of Harris's pit is unfavourably compared (K.P., p. 13) on account 

 of ' the absence of sand and the rarity of glauconite,' can only 

 refer to the 4 or 5 feet of gritty clay above the Mammillatus beds 

 in the Grovebmy pits, since the cla^^s of all the other sections 

 which- they describe are assigned by Dr. Kitchin & Mr. Pringle 

 to the ' Upper Gault.' But this peculiar gritty condition is 

 confined to the lowest bands onl}'- of the Lower clays ; it is present 

 all round the Shenley reef in the lowest layers of the Gault- filled 

 hollows, as I have shown, and is absent only on the bare top of the 

 reef (p. 67). So far as I can judge, the Lower clays above these 

 gritty layers are alike in all the exposures, with only such insigni- 

 ficant differences as one expects to find in passing from place to 

 place. 



In correlating the various sections of supposed 'Upper Gault,' 

 Dr. Kitchin & Mr. Pringle lay great stress upon two lithological 

 peculiarities as proofs of age : — 



(i) ' conspicuous small white nodules (white throughout) is a point to be 

 ' specially noted, since, owing to the rarity of fossils, the presence of these 

 ' nodules is helpful in identifying- these beds [that is, ' Upper Gault Clay ' and 

 'Basal bed of Upper Gaiilt '] in other sections' (K.P., p. 57) ; and (ii) 'im 

 ' perfectly bedded, crumbled, grey clay .... of a peculiar type .... made up 

 ' of innumerable small pellets, which are for the most part somewhat angular 

 ' in shape. It might be termed a finely brecciated clay' (K.P., p. 58). 



So far as I can discover, the ' small white calcareous nodules ' (i) 

 referred to are the knots of ' race,' produced by recent Aveathering 

 and segregation of lime where the calcareous cl^js approach the 

 surface. This ' race ' is exhibited in varying quantity, usually at a 

 depth of 2 to 5 feet, in the top clay of most of the Gault sections, 

 without relation to the stratigraphical horizon ; it was plentiful 

 in the clay just above the Mammillatus bed in Pratt's pit at 

 Grovebury (p. 35), occurring also in other sections at this level 

 (p. 30) ; it is most abundant where the beds have been affected 

 by ' creep.' 



The 'brecciated clay' (ii) appears to be the superficially dis- 



ZY 

 turbed clay ( — of my sections) seen above the bedded Gault in 



most places where the clay-deposits come to the surface. This 

 structure is the normal result of ' surface-creep ' or ' trail ' in 

 breaking up and incorporating soft beds in the lower part of the 

 ' creep ' ; wherefore its supposed origin as ' the redeposited debris 

 resulting from the denudation of some previously formed, well- 



