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V E I 



the transition slate, which contains im- 

 pressions of algae or sea-weeds. A few 

 fronds of ferns have been found in some 

 of the transition rocks. " It appears, 1 ' 

 says Prof. Buckland, " that nearly at the 

 same points in the progress of stratifica- 

 tion, where the most striking changes 

 take place in the remains of animal life, 

 there are found also concurrent changes 

 in the character of fossil vegetables." 

 VEIN, (vena, Lat. veine, Fr. vena, It.) 



1. In anatomy, elastic tubes pervading 

 every part of the body, and conveying 

 dark or venous blood from the arteries to 

 the heart. The veins are larger and more 

 numerous than the arteries, and may be 

 compared to rivers, which, collecting all 

 the water that is not imbibed by the soil, 

 and reconveying it into its general recep- 

 tacle, the ocean, perform an analogous 

 office in the economy of nature. 



2. In geology and mineralogy, fissures in 

 rocks filled up by mineral or metallic 

 substances differing from the rocks in 

 which they are situated. Mineral reposi- 

 tories of a flat or a tabular shape, which in 

 general traverse the strata of mountains, 

 crossing the strata, and having a different 

 direction from them, and filled with mi- 

 neral matter differing from the nature of 

 the rocks in which they occur. Mr. 

 Bakewell, in his admirable work " Intro- 

 duction to Geology," says, " perhaps the 

 reader may obtain a clearer notion of a 

 metallic vein, by first imagining a crack 

 or fissure in the earth a foot or more in 

 width, and extending east and west on the 

 surface, many hundred yards. Suppose 

 the crack or fissure to descend to an un- 

 known, depth, not in a perpendicular 

 direction, but sloping a little to the north 

 or south. Now, let us again suppose 

 each side of the fissure to become coated 

 with mineral matter of a different kind 

 from the rocks of which the fissure is 

 made, and then the whole fissure to be 

 filled by successive layers of various me- 

 tallic and mineral substances ; we shall 

 thus have a type of a metallic vein. Its 

 course from east to west is called its 

 direction, and the dip from the perpendi- 

 cular line of descent its hading. Thus it 

 is said to hade or dip to the north or 

 south." 



Veins appear to have been originally 

 fissures cutting through different beds of 

 rocks, that have been subsequently filled 

 with metallic ores, intermixed with other 

 mineral matter, of a different nature from 

 that of the rock which is intersected. 

 Metallic veins are generally of a more re- 

 cent formation than the rocks they inter- 

 sect. They occur principally in the pri- 

 mary and transition rocks, but they are also 

 found in the lowest of the secondary series. 



As regards the geographical distribu- 

 tion of mineral veins, it is an established 

 fact, that while extensive plain countries 

 are totally destitute of them, there are 

 few mountainous districts in which they 

 are not abundantly found. It has been 

 very generally observed that the character 

 of metalliferous veins changes with the 

 structure of the rock through which they 

 pass. It is itot necessary that there 

 should be an absolute difference of rock, 

 such as from slate to granite : a change 

 in the hardness and general mineralogical 

 structure of the same system of rocks 

 will frequently cause alterations of the 

 vein sufficiently remarkable. Among the 

 best conditions for expecting to find fis- 

 sures filled not only with an abundance of 

 metals, but also with kinds most useful to 

 a civilized state of society, is the proxi- 

 mity of some mass of granite, porphyry, 

 green-stone, or rocks of that class, to 

 stratified rocks, such as slates and others. 



The depth to which metallic veins 

 descend is not known, all large veins 

 continuing beyond the reach of the deep- 

 est mine. The expense of working them 

 beyond a certain depth rendering it un- 

 profitable, and the influx of water impos- 

 sible, to proceed. They frequently con- 

 tain totally different ores at different 

 depths. 



Veins vary in width from less than an 

 inch to thirty feet and upwards ; some- 

 times the same vein at one part con- 

 tracting, so as to be almost lost, and then 

 expanding to an immense width. This, 

 however, is not always the case, some 

 veins continuing of nearly the same width 

 throughout. 



Werner supposed that veins had be- 

 come filled by matter descending into 

 them from above, in a state of aqueous 

 solution : Hutton, on the other hand, 

 imagined that their contents were in- 

 jected from below, in a state of igneous 

 fusion. A third hypothesis refers the 

 filling of veins to a process of sublima- 

 tion from subjacent matters of intensely 

 heated mineral matter, into apertures and 

 fissures of the superincumbent rocks. A 

 fourth hypothesis attributes these metal- 

 lic collections to segregation, or infiltra- 

 tion. Professor Buckland, in his wonted 

 delightful style, says, " Whatever may 

 have been the means whereby veins were 

 charged with their precious contents ; 

 whether segregation or sublimation were 

 the exclusive method by which the me- 

 tals were accumulated ; or, whether each 

 of the supposed causes may have ope- 

 rated simultaneously or consecutively in 

 their production ; the existence of these 

 veins remains a fact of the highest impor- 

 tance to the human race : and although 



