166 OBIGIN AND DEVELOPMENT OF OEE-DEPOSITS. 



contents will in general be greater than in the case of the 

 phreatic-waters. The incessant transfer of mineral matter from 

 below, through the constantly flowing action of deep-seated 

 springs is thus accounted for by Hunt. " The cooling of the 

 surface of the earth by radiation, and the heating (of waters 

 already there) from below, would establish a system of aqueous 

 circulation by which the waters penetrating this permeable 

 layer (the upper portion of the earth's crust) would be returned 

 again to the surface as the usual springs charged with various 

 matters there to be deposited."* Hunt applies the crenitic hypo- 

 thesis principally to explain the origin of the crystalline rocks — 

 including even granite. But as he saw quite well it is equally 

 applicable to the origin of ore- deposits, if not more so. But 

 the rationale of the process seems here to need some illustration, 

 which I will endeavour to supply. 



In the first place, it is evident that the constant flow from each 

 particular source needs a constant supply. Considering that such 

 outflows have been going on all over the world for ages, we may 

 assume that the supply now comes from the surface. It may be 

 derived directly from rain; except, indeed, in countries where rains 

 are altogether unknown ; or indirectly from bodies of water sup- 

 plied by the rains ; or from the sea. There are but two ways in 

 which this water can reach the subterranean sources of the ascend- 

 ing thermals, (l)by flowing through fissures («c^wfl? divisional 

 planes in the rocks which are in direct communication with those 

 deep-seated sources, from which currents of water are made to 

 ascend by heat — and (2) by percolating through the rock-substance 

 (ordinarily though potential divisional planes, but often between 

 the separate crystals and particles of which nearly all rocks are 

 composed). The first we may call canalicular, the second 

 interstitial circulation. At moderate depths the former will 

 predominate — at greater depths the latter — because open fissures 

 will be far fewer, and those which actually exist much narrower 

 in proportion as greater depth is attained : still, it is likely that 

 some fissures and actual openings may exist at all depths. The 

 question then naturally arises " How can surface water make its 

 way down below the natural water-level in any given district?" 



* Op, cit., p 131. 



