ESSEX COUNTY. 



241 



absorb oxygen, tlian that portion known as the Hall vein, and the rock is deeply stained in 

 many places with the peroxide of iron. The walls are very much contorted ; and at the open- 

 ing where the principal ore is raised, tlie thickness of the vein is rapidly diminishing, which is 

 one of the consequences of this contortion. Figure 64 is intended to illustrate this fact : 



At a, on the line c, d, the vein is eight feet wide ; while at h, the place from which the ore is 

 now obtained, it is only four. Although it obstructs the raising of ore, and is therefore an in- 

 convenience and a loss, yet there is no danger that the vein will be lost ; the walls may so far 

 approach as to come nearly in contact, yet they will probably recede again, and disclose a vein 

 below five or six feet wide. 



In cases where the ore is apparently lost, it will be well to examine the strata a few feet 

 distant ; for in some instances, as has been already stated, the overhanging mass of rock may 

 not form the true wall ; and if so, the vein will be found, as is suggested, at the right or left. 

 In section No. 65, 



65. 



the veins a, a, a, are separated from each other by the intervening masses of rock b, b. In this 

 case, a, a, a, will be found to unite below ; and in the progress of mining, the intervening 

 rocks will disappear, and leave a vein twice or thrice the width of either of the former single 

 ones. 



Another point worthy of attention, is the arrangement of the particles of ore in the veins : 

 they are disposed somewhat in parallel lines, forming an apparent stratification. Some por- 



Geol. 2d Dist. 31 



