54 F. L. Kitchin and J. Pr ingle — 



the ammonites recorded in the above Hst was seen. Many 

 ammonites were found in this upper bed of clay, chiefly in the form 

 of fragmentary casts ; but every one was a Hojylites of the interrwptus- 

 type. Several species are represented, and it is unnecessary for our 

 present purpose to attempt to name them critically. They display 

 no greater diversity than is seen among a number of distinct species 

 determined alike as Hoplites interruptus (Brongn.) in the chief 

 public collections. Belemnites minimus List, also occurred, and 

 among the few imperfect lamellibranchs found we recognized 

 Plicatula gurgitis Pict. & Roux. 



We believe that an almost complete passage from Lower Green- 

 sand to Lower Gault is shown here. Although the dividing-line 

 between the Lower Greensand and the tanlefurcata bed is clearly 

 marked, and has been described by Mr. Lamplugh as a '"' sharp 

 junction ", there is no appearance of any considerable break in the 

 series. The contrast lies in the change from the cross-bedded 

 character of the sands below to the horizontal bedding, with accession 

 of the clay-constituent, in the overlying bed. This might be inter- 

 preted as merely proclaiming a somewhat rapid transition to more 

 tranquil conditions of sedimentation. At Miletree Farm (No. 8), 

 however, the tardefurcata bed with gritty phosphatic nodules is 

 separated from the top of the cross-bedded Lower Greensand by 

 a 6 ft. bed of horizontally stratified fine sand of distinctive 

 character, indicating that there is probably a true stratal break at 

 Webster's Pit, though not one of any considerable magnitude. 



A comparison between the section at Webster's Pit and that in 

 Harrises Pit at Shenley Hill thus demonstrates how strikingly they 

 are contrasted in all essential particulars. In the neighbourhood 

 of Billington Crossing there is no sign of the beds C to G of Shenley 

 Hill ; that is, the brachiopod bed, the basal Upper Gault, the iron- 

 stone-bands, and the impure sands overlying the " silver-sands ". 

 The lithological development of the Gault Clay in the two sections 

 is so different as alone to cast doubt on the identity of these beds ; 

 while a study of the fossils proves that no correlation of any part 

 of the Gault in the two localities is possible. 



II. Sections near Shenley Hill. 

 Sections in the neighbourhood of Shenley Hill show that there, 

 also, the relations between the Lower Greensand and the Gault are 

 different from those seen at Billington Crossing.^ Only at one locality, 

 a pit on the north side of Miletree Farm (No. 8), have we found the 

 tardefurcata bed above the false-bedded Lower Greensand. In the 

 same remarkable section the Upper Gault is seen to rest discordantly 

 upon these earlier beds. Farther to the west, the Upper Gault, 



^ The difference was remarked upon by Jukes-Browne, who pointed out 

 that south of Leighton Buzzard there is a gradual passage down to Lower 

 Greensand, while in this more northerly development there is not. The 

 Cretaceous Rocks of Britain, vol. i, "The Gault and Upper Greensand of 

 England" (Mem. Geol. Surv.), 1900, p. 284. 



