366 



THE GEOLOGIST. 



wings. In place of a vein- stone, however, tliere are certain accom- 

 paniments of a pecnliar condition in the rock which are considered 

 by the miner as bearing nnfaihng testimony of the prosimity of ore ; 

 these .guides are called the " weigh-beds" (ee' e" e'" in diagram), and 

 are composed of soft decomposed limestone mnch resembling (although 

 possessing an entirely different chemical composition) the clayey 

 contents of the " slides," and often " cross-courses" associated with 

 the lodes in Cornwall, and there termed " flookan." The position of 

 these beds is immediately overlying the ore, both in the thick as well 

 as the thin beds (see lignograph), but particularly the latter, where 

 the "weigh" is said "to change into ore." The collective term in 

 use for the various mineralized portions of the saddles is " bearing 

 beds." Cutting across the saddles or bearing beds, as has already 

 been mentioned, are the east and west fissures called " lums ;" their 

 veins are usually of great magnitude, and are commonly entirely 

 filled with marl and decomposed limestone, although in the imme- 

 diate neighbourhood of the pipe-veins som^e ore proceeding from the 

 saddles is mostly found attached to the cteeks of the vein. 



But if there is a great change in the structure of the vein, and the 

 mode of deposition of the ore when the pipe- veins come to intersect 

 the bearing beds, the change in respect of the nature of the minerals 

 is greater still, the ore in the pipe and rake-veins being lead, while 

 that in the saddles and limestone is almost always copper ; some lead as 

 usually found at first in the saddles, but as the beds near the limestone 

 the proportion of copper ore invariably increases, until the whole 

 deposit consists of this mineral. The distance to which the ore is 

 deposited in the bearing beds laterally divergent from the point of 

 intersection of the pipes, amounts seldom to more than two or three 

 saddles' breadth on either side, although there is no rule in the case ; 

 the transverse deposits, i. e., those which are parallel with the saddle- 

 joints, either on the wings or in the troughs entered often as much 

 as eighty fathoms in one direction from the point of intersection 

 with the pipe and limestone, and inasmuch as the limestone as stated 

 above usually contains some ore at such points of junction, the saddJes 

 are in such cases said " to carry away the ore." 



The description of the mode of occurrence of the ore in the bear- 

 ing beds as well as in the pipe- and rake-veins, in the preceding 

 paragraphs is a fair resume, I believe, of the aggregate of the observa- 

 tions of the most experienced miners in the districts lying north, 

 west, and south of Alstonfield, both in Staffordshire and the neigh- 

 bouring county. 



From the consideration of appearances we naturally turn to the 

 causes which have produced them ; and although it forms no part of 

 my intention to give more in this article than something like a con- 

 nected account of the phenomena observed in these metalliferous 

 saddles, as entered among my notes, there are yet some questions 

 v(>spo(."i ing ilio liisionj of the facts which need a brief recognition in 

 lliis ])lace. It has already been assumed that the plication of the 

 beds has arisen from pressm'e laterally applied, and the origin of the 



