314 Utissell Imtkuiion . 



appears charred on each side. He stated Instances of this 

 in the county of Durham, and in Shropshire. Such phje- 

 nomena appear to indicate that the basalt had been ejected 

 into the fissure in a state of igneous fusion. 



The length to which dykes extend has in few instances 

 been traced, owing to the upper part being hid by a cover- 

 ing of loose earth or soil. They vary in width, from 6 inches 

 to 70 feet or more. Tlieir depth remains unascertained. 

 Veins of granitic and other rocks occur also amongst pri- 

 mary mountains. 



Metallic veins resemble dykes in their structure, but not in 

 their contents, beinsr filled with different metallic substances 

 in a state of ore, and intermixed with various crystals 

 and earths. . Mr. Bakewell described the contents of many 

 remarkable veins in F-ngland and other parts of the world, 

 and the extent and depth to which they have been traced. 

 He explained their inclination, position, and structure, by 

 various drawings and specimens. It appeared from his de- 

 scription, that the Eton copper mine has been worked to a 

 greater depth than any other mine in England, ore having 

 been lately got at the depth of 236 fathoms, or 472 yards. 

 Mr. Bakewell described the various states in which the same 

 metal is sometimes found in one mine, as native metal, or 

 as alloyed with other metals, or mineralized by oxygen, sul- 

 phur, or acids. 



The lecturer proceeded to observe, that the question *' In 

 ** what manner have metallic veins been filled with their 

 *' contents?" has greatly divided the opinions of Geolo- 

 gists. Dr. Hutton supposed that mineral and metallic veins 

 have been formed by the breaking of the solid rocks from 

 the expansive force of subterranean fires, and their contents 

 ejected into them in 3 state of fusion from below. Mr, 

 Werner supposes they are fissures produced by the shrink- 

 ing or drying of the materials of which rocks are composed, 

 and afterwards filled from above bv the metallic matter 

 in a state of solution. Both these theories, Mr. Bakewell 

 observed, were at variance with the appearances which mi- 

 neral veins present. 



The favourable reception which Mr. Werner's system of 

 the formation of metallic veins has met with, was, he said, 

 a striking instance of the extent to which an attachment to 

 theory can be carried, and close the eyes of its votaries to the 

 plainest and most obvious facts. Had metallic veins been 

 filled from abovj, by the metallic ores infused in a state of 

 solution, this solution mt.st at one time have covered the 

 whole earth, and the ores deposited by it would have filled 



all 



