Dr. J. W. Gregory — Fossils from the Lower Greensand. 101 



fully supported this conclusion. Mr. Jukes-Browne^ has also 

 recently pointed out that the Upper Greensand of Western Wiltshire 

 is really only a calcareous sandy facies of the Gault. Similarly it is 

 possible that the change from the sands characteristic of the Lower 

 Greensand to the clays characteristic of the Gault, happened later in 

 Surrey and the West of Kent than it did on the east coast. If so, 

 then the "Folkestone Sands" of Guildford and Dorking were still 

 in process of deposition after the formation of the last of the 

 Folkestone Beds, and while the Gault was being laid down in the 

 east of Kent. 



This question cannot be finally answered until a collection of 

 fossils has been made from the very base of the Gault in Eastern 

 Surrey, sufficient for the determination of the exact zone to which 

 this belongs. On the ordinary assumption, it ought to be the zone 

 of Hoplites interruptus. There are, however, I'easons to believe that 

 this zone is absent from the area to the south of London. In spite 

 of having watched whatever exposures of Gault I could find along 

 the line between Guildford and Caterham, I have never been able 

 to find any Ammonite belonging to a zone lower than that of 

 Hoplites splendens. Nor can I find any reliable record of the occur- 

 rence there of the fossils of the lower zones. 



Hoplites interruptus seems restricted in England to the Folke- 

 stone area and the Red Chalk. It has, however, been recorded ^ 

 from the Richmond boring. If this record be correct, so probably 

 also is the ordinary assumption as to the age of the " Folkestone 

 Sands " of Surrey. The fossil is stated to have come from the depth 

 of 1100 feet, while Hoplites splendens is recorded from a depth of 

 1128 feet. Such an inversion of the zones seemed improbable, and 

 this led to a search for the specimen on which this record was based. 

 The specimen is now in the British Museum (Natural History), and 

 Mr. G. C. Crick has kindly examined it. He reports that though 

 much broken its characters are distinct, and it is unquestionably not 

 an Hoplites interruptus, but a specimen of the large fluted form of 

 H. splendens. The interruptus zone is therefore still unrecorded from 

 the London area or to the south of it. 



The Ammonite in the core from the depth of 1128 feet is, however, 

 also a typical specimen of H. splendens, and occurs only 13 feet 

 above the base of the Gault. This species ranges from the 4th to 

 the 7th zone of the Gault. If we make the somewhat improbable 

 assumption that this specimen came from the very lowest possible 

 point at which it could have occurred, then zones 1-3 are reduced to 

 a thickness of only 13 feet. Thus either the three basal zones are 

 proportionally much thinner at Richmond than they are at Folkestone, 

 or else one or more of them is there absent. The latter view appears 

 the more probable, as it explains the absence of the fossils of the 

 same three zones from the line between Guildford and Godstone. 

 If so, as in this area, there is no unconformity between but a gradual 



1 A. J. Jukes-Browne, "The Geology of Devizes, with Remarks on the Grouping 

 of Cretaceous Deposits," Proc. Geol. Assoc, vol. xii. 1892, pp. 264-266. 



2 Quart. Journ. Geol. Soc. vol. xl. 1884, p. 736. 



