320 The Geology of Devizes. 
visits them can only see that once upon a time an excellent and 
interesting section was to be seen at the spot. 
I need not now say more about the Ferruginous Sands except to 
express a hope that the time may come when the Ironstone they 
contain may be utilised, and to point out that they were formed in 
very shallow water along the shore of an ancient continent which 
then lay to the west of Wiltshire. 
2. Gault. Above the Ferruginous Sands, and forming the lower 
part of the slopes below Roundway, Devizes, Potterne, Stert, and 
Urchfont, is a dark grey clay known as the Gault. The brickyards 
at Dunkirk, Caen Hill, Stert, and Lavington are opened in this 
clay, and its thickness in this district is from S8O0ft. to 90ft. 
To the unassisted eye a lump of the clay only seems to be fine 
dry mud glistening with minute particles of a silvery substance 
which we know to be Mica. By the aid of the microscope we learn 
that it chiefly consists of very fine mud, in which are scattered 
small grains of Quartz, flakes of Mica, particles of Glauconite, 
fragments of shell, and some perfect shells of the tiny creatures 
known as Foraminifera. 
The lowest beds are well exposed at Caen Hill and Dunkirk 
brickyards, the middle beds at Lavington, and the upper beds were 
formerly worked on the slope at Dunkirk, but are not now exposed ' 
at any place in the district. Here, again, we are indebted to Mr. 
Cunnington for collecting from an exposure that proved to be 
temporary ; for the fossils he obtained from this upper Dunkirk 
brickyard are not the same as those which can be found in the lower 
pit. At the latter the prevalent Ammonite is Am. interruptus, with 
its variety Am. Benettie and occasionally Am. Budeantii, while at 
the higher pit 4m. lautus, Am. tuberculatus, and Am. splendens were 
found; species which also characterise the upper part of the Lower 
Gault of Folkestone. 
3. Malmstone. The upper part of the Gault becomes marly and 
sandy, and passes up into a soft grey or buff sandy stone, which is 
known as Malm or Malmstone. This is a peculiar rock, which has 
not yet been found at any other geological horizon, but uniformly 
occurs between the Gault and Greensand throughout the counties 
