UNSTEATIFIED CONDITION. 113 



vein at Freiberg consists of layers of blende, quartz, fluor spar, 

 pyrite, heavy spar, calcite, each two or three times repeated, the 

 layers nearly corresponding on either side of the middle seam. 



The bands of a vein are far from uniform at different heights, even 

 when the width of the vein is constant ; and they vary exceedingly 

 through the contractions and expansions which take place at intervals. 

 The expanded portions may alone be banded, or consist of layers 

 parallel to the sides, or contain ore. 



The mineral or rock-material accompanying the ore in a vein is 

 called the veinstone, or gangue. The most common kinds of vein- 

 stone are quartz, calcite, barite, and fluorite. 



In studying veins, besides noting their extent, mineral character 

 and structure, it is important to ascertain their strike and angle of 

 dip. There is generally an approximate uniformity of strike in a 

 given region ; and frequently the direction is jiarallel to the principal 

 line of elevation in the region. The nature of the walls or adjoining 

 rock, and systems of faults, are other jxnnts that should receive close 

 attention. 



False veins. — False veins are fissures filled from above. They are 

 usually distinguished by the sedimentary nature of the material ; all 

 true dikes or veins arc occupied by crystalline rocks or minerals. In 

 a similar manner, earth and organic remains may be washed into 

 caverns or any open spaces in rocks, and so make, in the very body 

 of an old record, a false entry. 



Such openings maj r become filled, from above, either with sand or rock, or with 

 metallic ores. The lead ore of Wisconsin, Galena in Northern Illinois, and Missouri, 

 occupies, according to J. D. Whitney, great irregular cavities in the rock of the region, 

 a limestone, and is not in true veins. The same is the case with the lead ore of Derby- 

 shire and Cumberland, England: for, along with the ore, and especially near the lime- 

 stone walls of the cavities, or so-called veins, there are sometimes many fossils, partly 

 those of the enclosing limestone, but many those of later rocks, showing not only that 

 the filling in of the ore was from above, but also that it was much subsequent in time 

 to the origin of the limestone (p. 104). 



Again, some of the so-called veins of metallic or mineral material are only beds. 

 They have the aspect of veins, because the rocks have been upturned so as to make 

 the beds vertical, or nearly so, in position. The great "veins " of iron ore in northern 

 New York, and the Marquette region, Michigan, and of zinc-iron ore (franklinite) in 

 New Jersey, are examples. The rocks of the region are all metamorphic, and so is the 

 iron ore, which originally was a layer of uncrystalline ore much like those of the Coal 

 formation in Pennsylvania. Many of the metallic "veins" of the world, even those 

 of zinc, copper, cobalt, etc., arc properly metalliferous layers, somewhat disguised by 

 upturning and metamorphism. So also crystalline limestone, in northern New York 

 and Canada, sometimes appears to be in veins, and has been so described, when, in 

 fact, it is strictly in layers, and is one of the metamorphic stratified rock3 of the region. 



In the language of miners, — 



A lode is a vein containing ore. 



The liiinfjing wall of a vein is the upper wall when the vein has an oblique dip; and 

 the opposite is the foot-wall. 



