4^ GEOLOGY OF THE BRISTOL COALFIELD. 



filling up the fissures of a rock, it generally contains a large 

 deposit of iron, lead or other mineral. Even from the pure 

 dolomite at Clevedon, may be procured abundantly, specimens of 

 galena, copper, barium, and manganese. At Shipham on the 

 Mendips, large deposits of Calamine have long been known. 

 Haematite is always obtained from the conglomerate where it 

 comes in contact with the carboniferous limestone. It occurs 

 either in fine specular crystals or as an amorphous red earth. It is 

 often met with as pure ferric oxide, although, unfortunately for 

 the smelter, it is mixed with a large percentage of silica, from the 

 contiguity to the upper shales which as we have seen are very 

 sandy or gritty. 



The following [are some of the component parts of haematite 

 obtained from this neighbourhood. The usual average of metal is 

 from 40 to ^o per cent. 



The beautiful specimens of Gothite and Bristol Diamonds, sold 

 by the men on the Downs^ are collected whenever the conglomerate 

 IS opened. 



In many spots hollow geodes, or as they are locally called 

 '' Potstones,'' are found having their cavities lined with crystals of 

 Quartz, Celestine, or Calcite. 



It is was in this formation that Messrs. Riley and Stutchbury, 

 found the celebrated Dinosaurian remains, of which we have so 



