CHAPTER IV. 



ON THE FILLING OF MINERAL VEINS. 



1.04.01. Bearing in mind what precedes, the preliminaries for 

 the discussion of mineral veins are set in order. We have traced 

 the formation of cavities by the shrinkage of rock masses in cool- 

 ing or drying, by the movements and disturbances of the earth's 

 crust (which are far the commonest and most important causes), 

 and by dolomitization. The enlargement of such cavities by sub- 

 terranean circulations followed, and the general effect of waters, 

 cold and heated. The sources of the elements of the useful min- 

 erals were pointed out so far as known. All these general and in- 

 disputable truths assist in the drawing of right conclusions. It 

 should be emphasized, as will appear later, that mineral veins or 

 cavity fillings do not embrace all metalliferous deposits. On the 

 contrary, the deposits which either form beds by themselves, or 

 which are disseminated through beds of barren rock arid are of the 

 same age with them, do not enter into the discussion. They are 

 characterized by being younger than their foot walls and older 

 than the hanging. Their geological structure is far simpler, and, 

 as will appear in the discussion of particular examples, the work- 

 ing out of their origin does not so often carry the investigator into 

 the realms of speculation and hypothesis. And yet it is not to be 

 inferred from the prominence here given to the discussion of veins 

 that bedded deposits yield to them, in any degree, in importance. 

 Iron ores, for instance, are often in beds. 



1.04.02. Methods of Filling. Methods of filling were summed 

 up a very long time ago by Yon Herder and Yon Cotta, 1 as fol- 

 lows : 1. Contemporaneous formation. 2. Lateral secretion. 3. 

 Descension. 4. Ascension by (a) infiltration, or (b) sublimation 

 with steam, or (c) by sublimation as gas, or (d) by igneous injec- 

 tion. To these should be added the more recent theory of (5) re- 



1 Erzlagerstatten, 2d ed., 1859, Vol. I., p. 172. 



