376 



ME. H. HOME ON AMPTHILL CLAY Iff [Aug. I903, 



These fossils indicate that we have here a great mass of 

 Ampthill Clay, which has been removed from the parent-mass. 

 If we compare this bed with the Ampthill Clay as known in situ, 

 we find that : — 



(1) It is lithologically identical, both being 



Well-section near Biggleswade. 



ORDNANCE 

 DATUM 160 



10'- 6" 



Septarian, 

 Nodules s 



77'- 6' 

 83'- 6" 



94- 



I35-Q' 



180-6" 





BEDS 



. o ; o , : o 



Boulder Clay 



Ampthill 

 Clay 



(transpcjrted) 



Chalky 

 Boulder-Clay 



indicate a slow rate of deposition. 



dark clays with 

 selenite-crystals. 

 Although the 

 presence of sele- 

 nite-crystals is 

 of little value 

 taken alone (se- 

 lenite being met 

 with in the Kim- 

 meridge Clay and 

 to a much less 

 degree in the 

 Oxford Clay, the 

 crystals being 

 due to exposure 

 and oxidation), 

 the occurrence 

 is yet of some 

 significance, as 

 pointed out by 

 the late Thomas 

 Roberts. 1 



(2) The occur- 

 rence of Ammo- 

 nites eoccavatus is 

 common to the 

 Oxford, Ampt- 

 Q hill, and Coralli- 

 < an Clays,but that 

 ►5 form is not men- 

 j[j tioned as occur- 

 j>g ring in theKim- 

 meridge Clay. 

 w Many of the 

 g ammonites were 

 J covered with 

 Serpulw, as else- 

 where observed 

 in the Corallian 

 Beds, and their 

 presence would 

 Were the basement-beds of the 



Bed in Boulder- 

 Clay Drift 



Disturbed Gault 



Gault-Clay 



Sand 



Grey Clay 



Sandstone 



Sand 



1 Quart. Journ. Geol. Soc. vol. xlv (1889) p. 550 ; and ' Jurassic Eocks of the 

 Neighbourhood of Cambridge ' [Sedgwick Prize Essay for 1886] 1892, p. 36. 

 See also H. B. Woodward, 'Jurassic Eocks of Britain -vol. v Mem. Geol. Surv. 

 (1895) p. 137. 



