ORIGINAL ARTICLES. 



On an Inverted Mass of Upper Cretaceous Strata near 

 Leighton Buzzard, Bedfordshire ; and on an Overlap 

 of the Upper Gault in that Neighbourhood. 



By F. L. KiTCHiN, M.A., Ph.D., and J. Pringle, F.G.S. 



Contents. 



1. Introduction. 



2. The Section. 



3. The New Evidence. 



(a) Characters and Correlation of the GauU in Mr. Gregory Harris's Pit. 



(b) Comparison with other Sections in the District. 



i. Sections near Leighton Buzzard, 

 ii. Sections near Shenley Hill. 



(c) Identification of the strata between the " Silver-sands " and the inverted 

 mass in Mr. Harris's Pit. 



(d) Relations of GauU and Cenomanian at the main outcrop. 



4. Interpretation of the Evidence. 



(a.) Events during Cretaceous time. 



(6) Events during and since Glacial time. 



5. Summary of conclusions. 



1. Introduction. 



lyrR. G. W. LAMPLUGH and the late Mr. J. F. Walker pubhshed 

 ■^^ a paper in 1903 on a fossiliferous bed at the top of the Lower 

 Greensand, exposed in sand-pits at Shenley Hill, near Leighton 

 Buzzard.^ The bed in question presented points of considerable 

 lithological interest and was remarkable for its rich brachiopod- 

 fauna. Its position above the " silver-sands " of the Lower Green- 

 sand and below a capping of dark " shaly clay ", ascribed by those 

 observers to the Lower Gault, led to the conclusion that it belonged 

 to the top part of the Lower Greensand. The discovery of its fossils 

 was considered to throw welcome light on the faunal characters 

 of the latest Lower Cretaceous rocks in England, represented in 

 more southern counties by relatively unfossiliferous sands. 



The fauna of this bed of liniestone-lenticles raised questions of 

 much interest. While there was apparently an admixture of Lower 

 Cretaceous and Upper Cretaceous species, a considerable number 

 of the fossils present in the bed constituted an association of species 

 known in England only from the lowest part of the varians zone, 

 the basal Cenomanian as understood in this country. Such were 

 the large form of Terebratula biplicata J. Sow., T. ovata J. Sow., 

 Terebrirostra lyra (J. Sow.), Rhynchonella grasiana d'Orb., and Rh. 

 dimidiata (J. Sow.) ; also the echinoids Cardiaster latissimus Ag., 

 Catopygus columbariiis Lam., Echinohrissus lacunosus Goldf., and 

 Pyrina laevis Ag. These and other elements of the fauna appeared 

 to contradict the interpretation offered by Messrs. Lamplugh and 



1 G. W. Lamplugh & J. F Walker. " A Fossiliferous Band at the top 

 of the Lower Greensand near Leighton Buzzard " : Quart. Journ. Geol. Soc, 

 vol. lix, 1903, p. 234. 



