84 The Buried Paieozoie Rocks of Wiltshire. 
In these formations we find thick clays, shales, great masses 
of marine corals, limestone, and sandstone, some of which are well 
known from their commercial value all over the world as Bath, 
Bradford, Box, and Corsham building-stones, and are found and 
largely worked in the neighbourhood. 
After probably a very long period of further subsidence, termi- 
nating in the laying down of the Kimmeridge Clay, a reverse 
movement set in. A large amount of land began to appear with 
small lakes in the north, while in a deep sea to the south the 
Portland Limestone (so well known as a building stone), was being 
deposited, and the materials brought down by the river system of 
the northern continent were being laid down as the Purbeck and 
Wealden formations, containing the remains of land animals, fresh 
water shells, &c. 
At the end of this continental period another great subsidence 
took place, resulting in the conditions shown in map III., which 
shows the probable line of the sea-coast during the formation of the 
green sand. The great mass of clay, which we know as gault, 
must have been formed from the débris of the carboniferous rocks 
of Wales, probably brought down by rivers flowing into an estuary 
on the west and distributed on the floor of the ocean at its mouth. 
The shores and bottom of this sea gradually sank and the sea gained 
on the land until it probably reached Ireland, and only the largest 
mountains of Wales were uncovered, standing out as small islands 
in the great “ Chalk Ocean,” in the deep quiet waters of which the 
countless remains of small animals falling on the bottom gradually 
built up those enormous masses of chalk, which extend so far, and 
of which our well-known downs are the remains. To complete the 
history I ought, perhaps, to tell you something of the processes by 
which the palzozoic rocks of the Mendips have been uncovered 
again by the removal of the chalk which so long overspread them, 
but it is too long a story to enter upon now. 
Having thus roughly, and I fear in no very scientific manner, 
traced the history of the rocks from the old Palzozoic continent to 
those we now stand on, I should like to say a word or two on the 
important bearing these old rocks have upon us now in the present 
