10 THIRD REPORT — 1833. 



times forming a breccia, remains or impressions of organic bo- 

 dies, coal and rock salt substances of recent formation, and other 

 matters, which should appear to have come in from above. 



This theory obtained considerable attention, and was very 

 generally adopted from the time of its being made known ; and 

 it has, I believe, many adherents at this day, particularly among 

 miners or those who have much opportunity of actual observa- 

 tion. 



Hutton's Theory of the Earth was published afterwards, in 

 1795; and as his views regarding the operations employed in 

 the formation of the structure of the rocks differed entirely 

 from those who assigned to them an aqueous origin, so it will 

 readily be supposed that he would promulgate a new explana- 

 tion of the formation of veins. 



According to Playfair, this theory embraced the following 

 propositions : — 



It allowed that veins are of a formation subsequent to the 

 hardening and consolidation of the strata which they traverse, 

 and that the crystallized and sparry structure of the substances 

 contained in them shows that these substances must have con- 

 creted from a fluid state. 



It assumes that this fluidity was simple like that of fusion by 

 heat, and not compound like that of solution in a menstruum. 



It is inferred that this is so from the acknowledged insolu- 

 bility of the substances that fill the veins in any one menstruum, 

 and from the total disappearance of the solvent, if there was 

 any, it being argued that nothing but heat could have escaped 

 from the cavities. 



It is further maintained, that as the metals generally appear 

 in veins in the form of sulphurets, the combination to which 

 their composition is owing could only have taken place by the 

 action of heat. And, furthei", that metals being also found na- 

 tive, to suppose that they could have been precipitated pure 

 and uncombined from any menstruum, is to trespass against all 

 analogy, and to maintain a physical impossibility. 



It is therefore inferred, that the materials which fill the mi- 

 neral veins were melted by heat, and forcibly injected in that 

 state into the clefts and fissures of the strata. 



The fissures must have ai'isen, not merely from the shrinking 

 of the strata while they acquired hardness and solidity, but 

 from the violence done to them when they were heaved up and 

 elevated in the manner which the theory has laid down. 



Slips or heaves of veins, and of the strata inclosing them, 

 are to be explained from the same violence which has been 

 exerted. 



