M, mbhB'on the Discovery of Useful MineraU, 349 



cess, look for such repositories ; and if the repository has been 

 discovered, we shall be able to determine in which direction 

 we should direct our observations, in order to investigate its 

 continuation and its exact constitution, as the original locality 

 may not be adapted for conveying this information. The 

 operations with which we are to pi'oceed, in either case, are 

 well known ; and the circumstances will, after reflection, guide 

 us better than general rules. The subject is treated of in se- 

 veral Avorks, and more especially in the excellent Introduc- 

 tion to Mining, by Delius."' If the repository which we are 

 examining be a bed — ^that is, if it be conformable to the struc- 

 ture of tha mountain-masses and of the rock — its continuation 

 is easily discovered ; for, if we have carefully noted the nature 

 of the rock, and accurately observed the direction of the struc- 

 ture, we have obtained a sufficient guide to it. If the covering 

 on the surface does not adm.it of our following up the bed, we 

 must uncover it from distance to distance. If in this opera,tion 

 we wish to avoid any unnecessary expenditure of money and 

 time, we mvist be perfectly informed of the inchnation of the 

 repositories, and must combine this with the known relations 

 of the surface, in order that we may be able to determine, 

 from point to point, the line described by its outcrop. It is 

 self evident that this cannot be accomplished with the neces- 

 sary certainty vinthout some measuring operations, and with- 

 out some openings requisite for determining the amount of 

 the dip : and, therefore, attention must be paid especially to 

 the last, as they must afford data for the first. We are now to 

 search for the repository at one of the points determined by the 

 results of the previous investigation, and, when it has been 

 found, to continue tlie labour in the same manner until we meet 

 with it in a place to which our aim was particularly directed. 

 If we sliould not have found the repository at the first or any 

 other point, as is easily possible, owing to the variableness of 

 its direction and dip, which can be known from the direction 

 and dip of the neighbouring rock, when there is opportunity of 

 observing its position and structure, we must still not give it 

 up ; but, if the constitution of the mountain-masses, in respect 



* Section 1st, chapter ii., p. 1C3. 



VOL. xxvnr. no. lvi. — april 1840. 



