80 ME. G. W. LAMPLrGH ON THE JUNCTION OP [vol, Ixxviii, 



VI. SUMMAET. 



The paper, a continuation of one by the Author and the late 

 J. F. Walker published by the Society in 1903, describes about 

 twenty sections exhibiting the base of the Grault in sandpits and 

 other excavations around Leighton Buzzard and westwards at South- 

 cott. Little worth, and Long Crendon. 



(1) The variable * Basement beds ' of the Gault are ' condensed ' 

 deposits, strongly influenced by local conditions like the ' Tourtias ' 

 of Flanders, and falling mainly within the ' zone of Ammonites 

 mammillatus ' as recognized in Northern France (= zones of A. 

 regularis and A. tardefurcatus of a later Grerman classification). 



(2) The evidence bears out Jukes-Browne's suggestion of the 

 occurrence of a current-swept strait in this quarter during late 

 Lower Cretaceous times, uniting northern and southern sea-basins. 

 During the accumulation of the ' Basement beds,' a shoal in this 

 strait north of Leighton formed a reef capped by ferruginous ' pan ' 

 and breccia, with lenticular patches of shell-limestone preserving 

 a fauna of ' reef-facies,' while the deeper water to the south 

 gathered a stratum of gritty glauconitic loam and clay with 

 fossiliferous phosphatic nodules of the French ' coquins de sable ' 

 type. The transitional stages are visible in the sections. 



(3) The dark clays above the ' Basement beds ' belong to the 

 Lower Gault, here reduced to about half its thickness at Folkestone, 

 the same reduction being exhibited also towards the opposite edge of 

 the basin, in Northern France. These clays rest sharply on the 

 ironstone * pans ' of the reef, but usually pass downwards by gritty 

 intercalations into the glauconitic loams. Fossils other than 

 ' Belemnites minimus' and 'Inoceramus concentricus ' are scarce 

 and in a poor state, but are in agreement with the stratigraphical 

 evidence. " - ■ 



(4) The incoming of the Upper Grault, with keeled ammonites of 

 the 'rostratus' group and 'Inoceramus sulcatus,' is indicated in three 

 of the sections, of which, however, two are at present obscure. A 

 band of corroded phosphatic nodules, like those of the ' Junction- 

 Bed ' at Folkestone, occurs near the base of the division, and 

 marks a pause in the sedimentation. This band has yielded many 

 fossils. 



(5) The palaeontology of the deposits is discussed, and is held to 

 be in general agreement with that of the same succession in Northern 

 France. 



(6) A recent suggestion that the beds at Shenley Hill may have 

 been inverted b}'- Gllacial agency is fully considered, and shown to 

 be untenable. 



[March 31st, 1922.] 



