352 M. Amedee Burat on the 



rules ; and that the works, by being conformable to these 

 rules of allure and disposition, would have in their favour, 

 not indeed the certainty which may be attained in regard to 

 regular veins, but the maximum of chances that may be cal- 

 culated on by the theory. 



Those who have attacked the general principles of geology 

 as applied to mining, have never attacked them in the locality 

 where they have been established. To this immense mass of 

 facts derived from nine centuries of operations, they oppose 

 some particular facts observed in a single mining operation. 

 Most frequently they have opposed some abnormal veins to 

 this multitude of regular veins, without ever suspecting that 

 the apparent insufficiency of the theory may have no other 

 cause than the insufficiency of their own works and interpre- 

 tations. 



Let us admit, for example, that the veins of Poullaouen 

 and Huelgoat in Bretagne have gradually become poorer 

 in depth, and that numerous attempts have been unsuc- 

 cessful in finding the minerals at a certain level. Can 

 we conclude from this that it is generally injudicious to 

 seek veins at greater depths, and that the great princi- 

 ples of the science lead only to deception ? Will it not 

 occur to every one, however little conversant with the art of 

 mining, that the researches into greater depths may have 

 been ill conducted, or rather that they have not been suffi- 

 ciently developed, since in Saxony, the Hartz, and Cornwall, 

 many veins are found to be rich at a much more considerable 

 depth than that of the mines of Bretagne % 



In order to discuss the probable conditions which regulate 

 veins in regard to their depth, in the double relation of their 

 allure and thickness and composition, let us first apply the 

 theoretical ideas, and then consider the facts in connection 

 with the estimates which we may be led to form. 



The continuity of veins, according to their direction, has 

 been generally ascertained and measured, and these measure- 

 ments may guide us in our hypotheses respecting their con- 

 tinuity, according to the inclination. These veins being, in 

 fact, fractures produced in the crust of the globe by subter- 

 ranean causes, there must exist a certain connection between 



