232 ORIGIN OF METALLIFEROUS DEPOSITS. [XII. 



It is not, however, in all cases necessary to invoke the direct 

 action of organisms to separate from water the dissolved metals. 

 It often happens that the waters containing these, instead of 

 finding their way to the ocean, flow into kkes or enclosed 

 basins, as in the case of the drainage-waters of an English 

 copper-mine, which have impregnated the turf of a neighboring 

 bog to such an extent that its ashes have been found a profita- 

 ble source of copper. Under certain conditions, not yet well 

 understood, this metal is precipitated by organic matters in the 

 metallic state, but if sulphates are present, a sulphide is 

 formed. Thus, in certain mesozoic slates in Bohemia, sulphide 

 of copper is found incrusting the remains of fishes, and in the 

 sandstones of New Jersey we find it penetrating the stems of 

 ancient trees. I have in my possession a portion of a small 

 trunk taken from the mud of a spring in the province of 

 Ontario, in which the yet undecayed wood of the centre is 

 seen to be incrusted by hard and brilliant iron-pyrites. In 

 like manner the trees found in the New Jersey sandstone be- 

 came incrusted with copper-sulphide, which, as decay went on. 

 in great part replaced the woody tissue. Similar deposits of 

 sulphides of copper and of iron often took place in basins 

 where the organic matter was present in such a condition or in 

 such quantity as to be entirely decomposed, and to leave no 

 trace of its form, unlike the examples just mentioned. In this 

 way have been formed fahlbands, and beds of pyrites and 

 other ores. 



The fact that such deposits are associated with silver and 

 with gold leads to the conclusion that these metals have obeyed 

 the same laws as iron and copper. It is known that both 

 persalts of iron and soluble sulphides have the power of ren- 

 dering gold soluble, and its subsequent deposition in the 

 metallic state is then easily understood.* 



I have endeavored by a few illustrations to show you by 



what processes some of the more common metals are dissolved 



and again separated from their solution in insoluble forms. It 



now remains to say somewhat of the geological relations of 



* See Appendix to this paper. 



