258 
RHAXELLA-CHERT IN EPPING FOREST GRAVELS. 
O.D. (the highest terrace of the Thames Valley Drift), I found a 
typical pebble of my Monk Wood rock, containing casts of an 
Ammonite (probably a juvenile specimen of Cardioceras corda- 
tns ?) and of a bivalve shell (? Lucina ); and Mr. A. L. Leach, 
F.G.S., who conducted the party, was able at once to identify 
the specimen as being Rhaxella-Chert, derived from Jurassic 
rocks of Corallian age. 
This chert occurs in situ over a limited area at Arngrove, 
near Brill, in Buckinghamshire ; and has also been described 
from the neighbourhood of Scarborough, Yorks. In both 
localities, the geological horizon is the lower portion of the Coral- 
Rag, i.e., the Lower Calcareous Grit, immediately above the 
Oxford Clay. The minute coral-like structure is due to myriads 
of globate spicules of a tetractinellid siliceous sponge to which 
Dr. G. J. Hinde gave the name of Rhaxella perforata ; alike in 
the parent rock and in my Valley Drift pebbles many of the 
spicules have disappeared by solution, leaving minute spherical 
cavities surrounded by a delicate meshwork of the cherty rock. 
A full account of the rock and its mode of occurrence in Bucks 
is given by Dr. A. M. Davies, F.G.S. (in Quarterly Journal of 
the Geological Society, 1907), who describes it as a thinly bedded 
stone broken up in situ into roughly rectangular blocks, some¬ 
times as much as four inches square and i|- inches thick, but 
often smaller : and Mr. E. T. Newton, F.R.S., contributed a 
Note on the few Drift specimens of this chert in Proc. Geologists ’ 
Association, xx., 1907, p. 127. 
Dr. A. E. Salter found fossiliferous pebbles of Rhaxella-chert 
in the Cromer Drift, and Dr. A. Irving writes me that he has it 
rather frequently in the Upper Rubble Drift of the Stort Valley 
at Hockerill, near Bishops Stortford, at about 200 feet above 
O.D. 
I have myself met with this Chert, in addition to the places 
already mentioned, at Coopersale Common, one mile east of 
Epping, in high level gravel (at about 340 feet above O.D.) 
included by Prestwich in his “ Westleton Beds,” but which is 
not improbably, in my opinion, a continuation of the highest 
terrace of the Roding V alley Gravel referred to above. Recentlv 
(September to November 1913), a small temporary gravel-pit 
on the Uplands Estate at Loughton, opened for road-ballast, 
together with the adjoining Loughton Cemetery, has yielded 
