322 The Geology of Devizes. 
globules and spicules, but the amount varies greatly, and thin slices 
of the Devizes Malm have rather a confused structure on account of 
the large proportion of other mineral ingredients. 
The Malmstone is, therefore, an interesting rock, for we learn 
that at the time it was being formed this district was the bed of a 
sea which was inhabited by a large colony of sponges. Other 
creatures do not seem to have found the area a suitable abode, for _ 
larger fossils are scarce, except a small sea-worm, which built a 
coiled calcareous shell (Vermicularia). 
The Malmstone is well exposed by the entrance lodge to Broadleas 
House, and along the scarped slope of Devizes Old Park. It passes 
up into a soft Micaceous Sandstone, which also contains some siliceous 
spicules and globules, but is mainly composed of the inorganic 
ingredients, Quartz, Mica, and Glauconite. This Sandstone is ex- 
posed in many road cuttings near Devizes, and has yielded a large 
number of fossils. Of these at least three good collections exist, that 
of Mr. W. Cunnington, now partly in the British Museum and partly 
in the Jermyn Street Museum; that of the Messrs. Sloper, which I 
arranged and named last summer in the Museum of this Society ; 
and thirdly, that of the late Mr H. Cunnington, which has been 
purchased for the Oxford Museum. These fossils are important, 
because it is only near Devizes and Urchfont that this part of the 
series contains so many organic remains. It would seem that the 
conditions which were favourable to the growth of the Sponges did 
not suit the Molluscs and Echinoderms, but that when the former 
died out large numbers of bivalve Mollusca took possession of the 
sea-floor, while Ammonites of several kinds swam through the water 
above. 
The Sandstone passes up into buff and grey sands, at the top of 
which there is a course of hard dark grey Calcareous Sandstone. 
This is the lowest rock bed seen in the road cutting south of Devizes, 
and, as it was formerly quarried at Potterne for building-stone, it 
may receive the name of “ Potterne Rock.” This rock has yielded 
the same assemblage of fossils as the Sandstone below. The thickness 
of beds from the base of the Malmstone to this rock is about 70ft. 
4. Grey and Green Sands. Above the Potterne Rock are a set of 
