428 THE CRETACEOUS SYSTEM. CHAP. 



In descending from the gravelly surface deposit, we have about 

 10 feet of blue laminated clay, with the following fossils : 



Ammonites dentatus. Nucula pectinata. 



,, lautus. Inoceramus concentricus (large). 



Belemnites minimus. Plicatula pectinoides. 



Solarium conoideum. Pecten quinquesulcatus. 



Kostellaria. Balanus. 



Dentalium, probably D. decussatum. Cyclocyathus Fittoni. 

 Coniferous wood. 



Below these unequivocal gault layers the argillaceous deposits 

 are striated with short drift laminae of sand and small gravel. In 

 these, by careful search, I found specimens of the ammonites 

 mentioned above. These layers are about 5 feet thick, and gradually 

 pass upward into the ordinary gault d . 



Below these sandy layers is a more specially pebbly band, in 

 some places compacted together, in which I found what seems 

 to be Pecten orbicularis. This band agrees in position with what 

 may be termed the basement bed of the gault or the cap of the 

 lower greensand at Folkestone. 



A remarkable exhibition of a sand-rock with pebbles occurs in 

 cliffs against the Thames at Clifden- Ferry. It is traversed by oxide 

 of iron in nests, laminae, and veins running in various directions. 

 As far as the composition of the mass is concerned, this sand-rock 

 resembles somewhat the Shot over irony rocks, and somewhat the 

 pebbly lower greensand of Faringdon; but few fossils have been 

 found in it. 



Farther to the east, the iron-sand range becomes continuous by 

 Woburn, Ampthill, Sandy, and Potton, and conspicuous over the 

 broad plains chiefly formed on Oxford clay. The sandy series is 

 streaked with iron laminae in various forms, and generally stained 

 of ochraceous tints derived from the iron oxides. Some white 

 bands also occur. In this series it is rare to find any fossils ; but 

 towards the base of it appears a variable band of gravel, one foot 

 or so in thickness, which is literally filled with fossils, many of 

 them fragmentary, mostly water-worn. In a considerable pro- 

 portion of the fossils bones are recognized, from different kinds 



d In this part of the series, probably, occurred a fine specimen of Ostrea macroptera, 

 which came into the hands of my late friend Professor Walker, who resided at 

 Culham. 



