THE JURASSIC DEPOSITS WHICH UNDERLIE LONDON. 735 
of the Totternhoe Stone, I find it quite impossible to say where the 
one division ends and the other begins. Doubtless the Zones of 
Holaster subglobosus and Rhynchonella Martini are represented in 
these beds, but their limits it is impossible to define. hynchonella 
Martini and numerous fish-remains occur in the higher part of this 
division; while the lowest 50 ft. of it certainly belongs to the 
Chalk Marl, as is shown not only by its lithological characters, but 
by the presence of Ammonites varians and Hamites. A specimen 
of the Chalk Marl from the Richmond well from a depth of 919 ft. 
was found to contain nearly 50 per cent. of insoluble material, among 
which were many curiously incrusted sponge-spicules. 
These 220 ft. of grey chalk and chalk marl, with the underlying 
Upper Greensand, make up the Lower Chalk or Cenomanian of 
Continental geologists. At Dover this division is about 194 ft. in 
thickness *. 
V. Tue Upper GrREENSAND. 
In the case of several of the deep borings in the London Basin 
considerable doubt exists as to the thickness and limits of the beds 
which should be referred to the Upper Greensand ; but upon this 
point, fortunately, the Richmond boring affords perfectly satisfactory 
evidence. 
At a depth of 924 ft. from the surface there was a decided 
change from the dark-grey rock of the Chalk Marl to more sandy 
strata with much mica and numerous glauconitic grains, which 
continued with little change down to the depth of 940 ft. These 
strata yielded a few fossils, chiefly fragments of Pectens (P. orbicu-— 
laris, Sow., and P. wmterstriata, Leym.). The mineral characters of 
the beds, as seen in hand specimens and also in thin slices under the 
microscope, agree so closely with those of the Upper Greensand of 
Surrey, that not the smallest doubt can exist as to their belonging 
to that formation. 
The Upper Greensand at Richmond consists of three portions, 
which may be distinguished as follows :— 
ft. 
Chalk Marl. 
(@) Hard micaccous sandy rock ice... c=. cone ener eters 6 
Upper 13 Softenand, more marly, beds) ieiiscssce2s. se seen eee eaee 6 
Greensand. | (3) Harder rock, similar to (1), but containing more 
CLAM CONTLC aa salon ce seeaiclseaeieesifsnee alone aan 
Upper Gault clay. 
The beds (1) and (3) are quite undistinguishable in character and 
appearance from the well-known “ Firestone” of Godstone. They 
contain respectively only 14°5 and 12:5 per cent. of calcic carbonate ; 
the insoluble residue consisting of fine quartz-sand, mica, and 
glauconite. A characteristic specimen of Firestone from Godstone 
yielded on analysis 16-2 per cent. of calcic carbonate. 
The bed (2) is softer and approximates in character to the 
*“‘ Hearthstone” of the Godstone pits, a typical specimen of which 
was found to contain 38 per cent. of calcic carbonate. The Rich- 
* See F. G. H. Price, Quart. Journ. Geol. Soc. vol. xxxiil. (1877), p. 445. 
