Vol. 59.] AMPTHILL CLAY-BOULDER AT BIGGLESWADE. 



375 



Depth from 

 surface in feet. 

 2 



101 



m 



83i 

 94 



29. On a Tean sported Mass of Ampthill Clay in the Boulder- 

 Clay at Biggleswade (Bedfordshire). By Henry Home, Esq. 

 (Communicated by Horace B. Woodward, Esq., E.R.S., F.Gr.S. 

 Read June 24th, 1903.) 



The section to be described has been exposed in the construction of 

 a well, which is being sunk into the water-bearing strata of the 

 Lower Greensand, about 2 miles south-south-east of Biggleswade 

 Railway-station, and less than half a mile north of Bleak Hall on 

 the western side of the Roman "Way. The excavation down to the 

 70-foot level was about 14 feet in diameter, and below that depth 

 about 10 feet. 



The section is as follows (see also fig., p. 376) : — 



Thickness 

 in feet. 



1. Agricultural soil 2 



2. Boulder-Clay .- 8£ 



3. Dark indigo-coloured clay 67 



4. Chalky Boulder-Clay 6 



5. A bed in the Boulder-Clay drift 10£ 



6. Passage-bed to Gault 7| 101f 



7. Gault-Clay 7£ 109 ^ 



8. Lower Greensand to the level of 180|- feet, not bottomed. 



Bed No. 1 calls for no remark. 



Bed No. 2 contains well-striated boulders and fossils, chiefly 

 belemnites and Gryphcece of the Oxford Clay and Lower Lias. 



Bed No. 3 : thickness 67 feet. On the excavation entering this 

 bed it was seen that the clay had not the characteristics of the 

 Gault. It was a dark indigo-coloured selenitiferous clay, laminated, 

 and becoming shaly on exposure to dry weather. A large number 

 of septarian nodules occurred throughout it, some in regular layers 

 parallel to the bedding of the clay, and others irregularly. 



One layer of which special notice was taken, situated at a depth 

 of 37 feet from the surface, dipped west-south-westward at an angle 

 of 9°. Some of these septarian nodules had an area of as much as 

 20 square feet and weighed about 2 tons. They nearly all contained 

 water. The characteristic fossil that was found throughout the 

 greater part of this bed was Ammonites (Cardioceras) excavatus, 

 which occurs also in a pyritized form. Thracia depressa too was 

 present at all levels. 



The following fossils obtained from this bed, between the depths 

 of 10! and 7?2 feefc > were identified by Mr. E. T. Newton, F.R.S.:— 



Ammonites (Cardioceras) excavatus, 



Sow. 

 Ammonites (Perisphinctes) varicos- 



tatus, Buckl. 

 Belemnites allied to Panderi, d'Orb. 

 Belemnites cf. nitidus, Dollfus. 

 Gfasteropod. 

 Kucula sp. 

 Pleuromya recurva, Phil. 



Pleuromya recurva, Phil, (small form). 



Protocardium sp. 



Trigonia near to clavellata, Sow. 



Trigonia near to triquetra, Seeb. 



Ostrea deltoidea, Sow. 



Ostrea discoidea, Seeley. 



Thracia depressa, Sow. 



Serpula tetragona, Sow. 



