MINERAL VEIN8. 



MINERALOGY. 



Fault*, or fissure* accompanied by dislocations, offer, in addition 

 to all the feet* already mentioned, the very important information that 

 lit* crust of the earth baa been broken at different time*, a* well an in 

 different direction!. In the drawing of two intersecting vein*, which 

 illustrates thia article, it will be seen that the vein No. 2 cuts through 

 and displace* the strata, which had been already broken and displaced 

 by the rein No. 1. The relative antiquity of these two veina baa been 

 generally allowed to be in the order of the number*. Now a* the 

 ntetalliferoua oontenta of the fissures No. 1 are divided by No. 3, ai 

 well aa the atrata which bound it, there appear* reason to conclude 

 that the rein No. 1 wai filled with ita mineral content* before the 

 disturbance of the ground by the Ensure No. 2. 



We are thna conducted tu the remaining part of the general inquiry 

 proposed, namely, the cause* concerned in filling the cavities of all 

 kin. In, already classed. The evidence of the dislocation of strata on 

 the side* of most mineral veins leads, when generalised, to the recog- 

 nition of several (ystoms of veins, even in one district, of unequal 

 antiquity. It is also found that these systems pass in different 

 directions respectively, one set east -north -east, another north- 

 north-west, others to intermediate points; and further, there are 

 observed in these systems of veins unlike in direction, and unequal 

 in antiquity some general and characteristic differences m the contents 

 of the veins. 



Werner gives eight successive systems of veins in the Freyberg 

 Mines, but the definitions are far from clear. M. Came gives eight 

 successive groups of veins and slides in Cornwall, more clearly 

 characterised ; the oldest are tin .veins (lodes), underlying (dipping) 

 to the north, ranging nearly east and west by compass. The second are 

 tin veins, underlying to the south, ranging east and west nearly (by 

 compass). The third includes east and west copper reins. The 

 fourth are diagonal (or contra) veins, ranging north-west and south east, 

 and yield copper. The fifth class includes cross-courses, ranging north- 

 north-west and south-south-east, and rarely yielding metal, except lead. 

 A sixth group yields copper. A seventh includes ' cross flukans ' (clay 

 veins), ranging nearly north and south, and an eighth, the 'slides,' 

 which are formed of soft clay, and cut through all the others. 



This classification, though too hard and precise for exact adaptation 

 to nature, is valuable as an index to many complicated phenomena ; 

 bat the relative antiquity of so many seta of fractures is a difficult 

 problem, requiring much mechanical science, and a knowledge of the 

 relative hardness and resisting power of the masses broken. .Sir 11 . 

 De la Beche has shown ('Ordnance Report on the Geology of Cornwall,' 

 Ac., p. 299) a simple case of this nature, in which the intersecting 

 elvan dyke is probably not the newest of the two fractures. In the 

 elaborate volume just quoted the reader will find a vast body of 

 digested information regarding the phenomena of the Cornish and 

 Devon mineral veins. As a combined result, we find in the veins of 

 Cornwall a manifest tendency to two sets, one (the oldest) east-north- 

 east, yielding most of the ores, the other north-north-west, crossing 

 the preceding almost from sea to sea. In Devonshire also two sets 

 appear, one (the oldest) nearly east and west, yielding most of the 

 ores, the other north and south, crossing the other. Continuing the 

 investigation, we find this system of cross courses (ranging north and 

 south) extended into Dorsetshire, and there dividing the chalk, so that 

 a comparatively recent geological date for some of the great cross 

 courses of Devon and Cornwall may be probably inferred. Adopting 

 the views of this author, we find evidence of four systems of east and 

 west frocturei in the district of Cornwall and Devon : 1. That of the 

 upheaval of granite, and the arrangement of the strikes of the beds 

 of slate. 2. The elvan (porphyry) courses, which traverse alike the 

 granite and the strata disturbed with it 3. The east and west sys- 

 tems of veins. 4. The system (indistinctly traced) of east and west 

 clay slides ; and adding to them tho north and south traps, elvann, 

 cro courses, and flukans, we see clearly how many and various have 

 been the fractures and fissures, and how complicated the conditions 

 under which these fissure* were stored with their content*. What 

 was the agency by which this was acccomp)ihed f 



Werner (1791) believed that fissure* were filled from above, by 

 precipitations of earthy and metallic salts held in solution by waU-r. 

 As some of the substances common in mineral veins are not known to 

 be soluble in water, separately or in combination, we can only adopt 

 this view upon the supposition that the crystallisations in veins are 

 the result of double decomposition* in the liquid ; nor even with this 

 aid is the process at all clear by which the metallic masics were 

 formed. 



Lehman had previously (17.18) Introduced the notion of lublimed 

 vapour* and exhalations ; and if we believe that sulphuretted hydro- j 

 gen gas was abundant in these, the formation of sulphurets from salts j 

 of lead, copper, ftc. might become a possible case. Neeker revived ' 

 thi* idea. ('OeoL Society Abstract*,' 1832.) Dra. Button and Play- , 

 fair maintained that the vein-spars and metallic ores were injected into 

 fissures not in a state of solution in water, but in a state of fusion ' 

 through heat. They were a sort of metalliferous dykes. 



In consequence of the experiment* of Mr. Fox, which show in 

 certain case* the passage of electrical currents between different parts 

 of the metalliferous veins of Cornwall, and an augmentation of tem- 

 perature in them a* we descend into the earth, a fourth general view 

 ha* gradually and obscurely grown up to importance. In this view 



electrical forces are appealed to for determining the deposition of 

 matter brought into the fissure* by water operating on metallic aggre- 

 gations, at great depths and under considerable heat Such heated 

 water* would circulate upward* and downwards in the open spaces of 

 the rocks ; in the upper parts of the fissure* they would b cooled, 

 and might deposit part of their dissolvent contents ; these would be 

 arranged by electrical affinities under the influence of the various 

 nature, direction, and Closuring of the rocks. 



Such affinities might be dependent on local electrical currents, 

 generated by the local differences of the rocks and minerals, or on t h 

 general terrestrial currents which govern common magnetism, or on a 

 combination or opposition of these. Under any circumstances, 

 evidence of these general currents must be looked for in the general 

 phenomena, and the local currents must be sought in the local pheno- 

 mena. Adopting this theory as at least partially true, we may venture 

 to refer to general currents the remarkable fact of the frequent 

 arrangement of metals in east and west veins, or in veins pointing a 

 little north or a little south of east and west ; for within such limits: 

 in European and Mexican latitudes these general electrical currents 

 may be conceived to pass, varying most in Europe, according as the 

 polarities varied from time to time. We may refer to local currents 

 the limitation (which is seldom really, though often in appearance, 

 arbitrary) of the metallic contents of a vein to particular adjacent 

 rocks, to particular oblique parallel shoots or pipes, to particular sides 

 or ends of a vein, to particular depths, or particular nidiform masses. 

 To a succession of such operations we may refer the successive vertical 

 lamination of several sorts of crystals (fluor, carbonate of barytas, 

 lead-ore, blonde, &c.) in the same vein ; and after a principal vein was 

 partially filled, we may conceive without difficulty the deposition <( 

 nearly similar contents in neighbouring fissures or joint*, or even 

 closed cavities, if these should then become the lines of easiest 

 electrical conduction. 



The reader will find a comprehensive view of this hypothesis 

 compared with characteristic phenomena in the ' Ordnance Report on 

 Devon and Cornwall' Indeed anything approaching to the strict and 

 severe process of deductive reasoning from known physical truths, 

 applied to conditions like those ascertained in the districts of Cornwall 

 and Aldstone Moor, has been hardly attempted elsewhere. Yet the 

 occasion is favourable. Sir H. De la Beche has embodied a vast mass 

 of available results in the Report already quoted. Mr. Fox has expe- 

 rimentally almost made mineral veins by imitating the natural 

 arrangements of the rocks of Cornwall : the electrotype process is 

 daily revealing new and unexpected phenomena of electrical transfer 

 under manageable conditions ; and there are these great inducements 

 for an earnest general investigation of the whole subject, that in the 

 first place crystallography and the doctrines of molecular forces would 

 assuredly be advanced by it ; and, what is still more important, laws 

 of judgment and practice in mining operations would be satisfactorily 

 established and confidently applied to cases entirely beyond the range 

 of ordinary experience. We must however caution the reader who 

 prefers this new view of the origin of veins against any contemptuous 

 disregard of the opinions of Werner, Lehman, and Hutton, on the 

 ground of special difficulties in regard to solutions iu water, subli- 

 mations of vapours, or igneous fusions of minerals. There is abun- 

 dance of facts known to redeem their speculations from a hasty charge 

 of absurdity ; there are many insulated facts which seem to agree 

 with them ; and at all events the descriptions furnished by Pryce, 

 Werner, Carne, Fournet, Fox, Henwood, Taylor, and De la Beche, 

 must be carefully and respectfully considered, and combined with the 

 general laws of the earth's structure and established principles of 

 physics, before we can boast of a theory of Mim-nil Veins. 



(Pryce, Mineralogia Cornubiauil; Werner, On Veint, 1791 English 



edition, 1809 ; Hawkins, Carne, Davy, and others, in Transaction* of 



the Geological Society of Cornwall ; Williams, Mineral Kingdom ; 



Fournet, in D'Aubuisson's Geology, vol. iii. ; Fox, in Proceeding! of 



linic Society ; Henwood and Neeker, in Aliitractt of Geoloyical 



Society of London, 1832; Taylor, in Report to British Auoci 



1833; Becquerel Traitt <f Electricitf , 1885; Murchison, Marian 



Syitem ; Phillips, in Lardner's Cyclopedia, 1889; De la Beche, 



Ordnance Report on Cornwall, Deron, antl \\'ot Somerict, 1839; Lyell, 



i:la of Ueol'Kjy.) 



MINKHAI. i V, according to the definition given by Kirwan, is 

 the art of distinguishing mineral substances from each other. It in:iy 

 bo regarded both a* a science and an art : as a science, in reference to 

 the knowledge requisite for supplying accurate descriptions of minerals, 

 and forming what may bo termed a natural classification ; and an art, 

 in reference to the arrangement of the descriptive characters for the 

 purpose of afterwards distinguishing minerals from each oilier. 



Mineralogy then must be considered as including the chemical 

 coiujionition of bodies, and an account of their external or physical 

 properties. Both are requisite, for substance* occur which agree in 

 their chemical composition, and exhibit differences in their external 

 characters; while there are other bodies which differ in their chemical 

 constitution, but agree in their external properties. 



Various methods of arrangement of minerals hare been proposed by 

 different authors. According to Werner, minerals were divided into 

 the four classes of earthy minerals, saline minerals, inflammables, and 

 metal*: Karsten classed them under the heads of earths, salts, com- 



