198 Mr. Webster on the Strata lying over the Chalk. 



The bottom of the shaft was 30 feet under the bed of the river 

 Thames. The unfortunate failure of the project, from the river 

 bursting in before they had completed a drift, is well known. 



At Reading there are several pits dug for the purpose of procuring 

 brick clay, some of which reach to the chalk ; an account of the 

 strata at this place is given us by Dr. Brewer in the Phil. Trans. 1800. 

 -- Immediately incumbent on the chalk is a stratum 2 feet thick of 

 green sand containing numerous oyster shells. Many of these are 

 entire, having both their valves united ; but the animal matter being 

 entirely gone, and the shell not having undergone the process of 

 petrifaction, they are white and extremely brittle, and separate into 

 laminse. Fishes teeth are also found with them. Over this is a bed 

 3 feet thick of a bluish rough clay, then fuller's earth 2j feet 

 and fine white sand 7 feet. Next is a stiff red clay, probably the 

 plastic clay, of which tiles are made. This is much thicker than any 

 of the other beds ; and over is the alluvial soil. These strata are 

 known to extend for several miles with little variation. 



At Brentford, on the borders of the Thames, about 6 miles from 

 London, many important discoveries have been made in the grounds 

 of Mr. Trimmer ; an account of which has lately been read before 

 the Royal Society. Here the chalk lies at a great depth, as they 

 have dug 200 feet through the blue clay without coming to it. Im- 

 mediately upon this clay are a few feet of sand and gravel with 

 water ; over that from 1 to 9 feet of calcareous loam ; then sandy 

 gravel 7 feet, and lastly calcareous loam or common brick earth 

 9 feet. In the blue clay were found the usual fossils of this 

 stratum, being entirely marine. The three beds just over it con- 

 tained a vast collection of the bones of elephants, both African and 

 Indian, of the hippopotamus, the horns and jaws of oxen, the horns 

 of deer, and both land and freshwater shells. 



