736 PROF. J. W. JUDD ON THE NATURE AND RELATIONS OF 
mond rock contains 19°5 per cent. of calcic carbonate, the insoluble 
residue containing less sand but more argillaceous matter than the 
beds above and below it. 
VI. Tue Gavrt. 
The change from the glauconitic sandy beds of the Upper Green- 
sand to the marly clays of the Upper Gault is very well marked in 
the Richmond boring. The base of the Lower Gault is also un- 
mistakably defined by the usual band of phosphatic nodules. In 
this way the Gault is proved to extend from the depth of 940 ft. to 
that of 11413 ft. from the surface, and to have a thickness of 
2014 ft. 
It thus appears that the thickness of the Gault at Richmond 
exceeds that found in any of the other deep London wells, which 
gave the following results :-— 
ft. 
Kentish Dowie. 2 ees oes ee tee 1303 
Tioughton. Giissex))\ 2533220 ee. were edocs 1323 
Menuz’s Brewety cots ee eee 160 
Ware. 42.5 coeecent eee cece tine or ee eee ae 160 
Turnford, near Cheshunt .......... St eee 161 
Crossness, néar giriths h..2.0. nl 176 
For this result, however, we were not unprepared, for many facts 
point to the conclusion that along the base of the North Downs the 
Gault clay has a very considerable thickness, and that this thickness 
much exceeds that which is indicated on the maps and sections of 
the Geological Survey. This conclusion has been confirmed by the 
well at Shoreham, near Sevenoaks, where the Gault was found to be 
at least 226 ft. in thickness, and by that at Caterham Waterworks, 
where it was no less than 343 ft. The development of the Gault 
at Richmond is therefore just what might have been anticipated. 
In the Gault of Folkestone, which is less than 100 ft. in thickness, 
there occur several bands with phosphatic nodules and remanié 
fossils, doubtless indicating interruptions of greater or less duration 
in the process of sedimentation. These junction-beds have proved 
of much service as indicating the limits ef the different zones into 
which the Gault has been divided by Mr. De Rance and Mr. Price. 
Fossils were tolerably abundant in the Gault cores from Richmond. 
The most common, with the exception of fragmentary and unde- 
terminable fish, crustacean and echinoderm remains, which were 
found at many different horizons, are given in the following list, 
with the depth at which they occurred :— 
Hamites armatus, Sow. (? elegans, d’ Orb.) (940 ft.). 
Ancyloceras spinigerum, Sow., sp. (1104 ft.). 
Ammonites splendens, Sow. (1128 ft.). 
Ammonites Bouchardianus, d’Orb.? (1059 ft.). 
Ammonites rostratus?, Sow. (1662 ft.). 
Ammonites interruptus, Brug. (1100 ft.). 
Inoceramus concentricus, Sow., abundant (967 ft.). 
Nucula, sp. 
Pentacrinus Fittoni, Azst. (990 ft.). 
Many species of Foraminifera. 
Plant remains. 
