1006.] on Ore Deposits and their Distrihution in Depth. 311 



have found it in far smaller quantities than Professor Liversidge has 

 obtained. 



But if gold be present in sea water to the amount of only a grain 

 to the ton, the gross amount is temptingly large, for it has been 

 calculated that at that rate, there is enough gold in the sea to supply 

 every human being with the useless dowry of 75 tons of gold. 



Geologists accept the presence of gold in the sea on the authority 

 of the chemists. But that the sea is the source of the gold in our 

 lodes is a very different matter. The amount of gold in the sea is so 

 small that it does not appear to follow the ordinary processes of 

 precipitation. Gold is a metal that is very readily precipitated from 

 solution. It is most likely present in the sea as some chloride, and 

 gold is thrown out of chloride solutions by the action of light in the 

 presence of organic matter. But some careful analyses of mud from 

 the sea-floor, at positions where gold should be steadily precipitated 

 by these agencies, have shown no trace of it. 



Moreover, the essays of Dr. Don, confirmed by those of Mr. 

 W. H. Bailey in the laboratory of the Mines Department of Victoria, 

 have shown that the slates, from which the quartz lodes were 

 supposed to have got their gold, contain none, except when they also 

 contain pyrites : and the microscope proves that the pyrites was 

 formed after the rock, and the gold was doubtless introduced 

 simultaneously with the formation of the pyrites. 



It is, in fact, far more probable that whatever gold the sea may 

 contain was dissolved from the land, than that the gold on the land 

 was derived by precipitation from the sea. 



Igneous Eocks as a Source of Okes. 



;-The igneous rocks are natural sources of iron and its allied metals, 

 for iron is an essential constituent, often to a considerable extent, 

 of the basic igneous rocks. Iron, moreover, is a material which, in 

 the ample time available for ore formation, is easily rendered soluble 

 by natural agencies. Hence the w^eathering of basic igneous rocks 

 gives an ample supply of iron. It is removed in solution and re- 

 deposited in the films of rust, which colour red sandstones, and 

 yellow sands and loams. Iron is the most widely diffused of all colour- 

 ing matters ; but rocks in which it may be conspicuous as a pigment, 

 may be of no use as an ore. A deposit is no commercial value as an 

 iron ore unless it contains at least 30, and usually from 50 to 60, per 

 cent, of iron. But the agencies that have leached out the iron from 

 igneous rocks, and with it painted our landscapes, continue their 

 action, and concentrate the iron as a serviceable ore. 



Thus, the precipitation of iron carbonate by organic agencies in 

 swamps, in lagoons, and along muddy shores, forms beds of clay 

 ironstone, such as the black band ironstones associated with our coal 



