112 ORIGIN AND DEVELOPMENT OE ORE DEPOSITS. 



Reference has been made to the dense atmosphere surround- 

 ing the globe in its early stages. The more condensible vapours 

 of this atmosphere would be rapidly and continuously precipitated 

 on the newly formed crust, in proportion to the progressive 

 lowering of the temperature, partly as solids, more largely, in all 

 probability, as liquids ; and so the first separation of land, sea, 

 and sky would result ; each somewhat resembling their present 

 counterparts, each, no doubt, differing in many important 

 particulars, yet subject to the same general laws. With solid, 

 liquid, and vapour in juxtaposition, gravity would of necessity 

 gather the liquids into the low places to form seas, in which 

 there could not fail to be, as now, tides and currents. The 

 atmosphere would be violently agitated by storms, and the 

 elevated portion of the dry land would be fractured by unequal 

 contraction and expansion, worn away by heavy rains gathering 

 into torrents and rivers, dissolved by corrosive fluids, and broken 

 up by electric and crystallizing forces. All these pheDomena 

 might be expected to prevail precisely as at present, only with 

 greatly higher intensity ; and the detrital deposits so formed, 

 mingled with and consolidated by chemical precipitates from 

 the highly-charged waters, would form the first truly stratified 

 deposits. 



Such early sediments, formed under such conditions, would 

 of necessity differ greatly from those formed at later periods, 

 when the earth, sea, and sky had all become considerably cooled 

 down, their youthful energies, so to speak, moderated ; but, 

 though in all probability highly crystalline, they would be true 

 sedimentary rocks notwithstanding, and subject to the same 

 mechanical and physical laws as their latest successors. 



Various origin of rock-masses. All rock-masses when first 

 formed may be regarded as original, although their materials 

 may have been derived from pre-existing rocks. It will be 



beneath, he observes that the data at our disposal are at present too scanty to 

 positively determine any of the shares quantitatively, and concludes, " Who shall 

 presume to assign quantitative shares (+ or — ) to (1) contraction due to meta- 

 morphism in the solid underlay ers. (2) expansion of the rocks under increment 

 temperature, (3) formation of geoclines (linear systems of folding and contortion) 

 by lateral pressure, (4) contraction and expansion on melting and solidification, 

 (5) effects of pressure on the water-gas contained in the fluid magma, (6) the 

 differential load on a flexible crust." 



