84. 



The Buried Palceozoic RocJcs 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 debris 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 palaeozoic 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 Palaeozoic 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 



