VOLCANISM AND ORE DEPOSITS. 1015 



Second. The igneous rocks may furnish aqueous and gaseous solutions 

 which transport the metals to their places of deposition. It is very difficult 

 to determine the quantitative amount of the solutions of this sort. Where 

 the igneous rocks are intruded in the zone of fracture, or appear at the 

 surface in the ordinary forms characteristic of volcanism, it is impossible 

 to discriminate the gaseous and aqueous material which has always been 

 within the magma from the solutions which have derived their water from 

 meteoric sources or from the sea. It is certain that vast quantities of 

 water of meteoric origin pass into the zone of fracture. In connection 

 with the water phenomena of volcanic action it may perhaps be doubted if 

 the water from the sea is important ; but there can be no question con- 

 cerning the effect of water of meteoric origin. Where voluminous hot 

 springs issue in connection with present or past volcanic action all the 

 evidence indicates that the major portion of this water is of meteoric origin 

 (pp. 1065-1069) However, it has been pointed out (pp. 661-668) that 

 in the zone of anamorphism the conditions are very different. It can not 

 be assumed that there the water is abundantly derived from meteoric sources. 

 In' connection with batholitic action it has been shown that there is complete 

 gradation between strictly igneous material and material which is apparently 

 deposited from solutions. It has been explained that the water which does 

 this work is probably in considerable part derived from the magma itself, 

 although some is doubtless included between the mineral particles and some 

 is produced by processes of dehydration. But even for this zone it is 

 impossible to make any quantitative statement as to the relative amounts of 

 water concerned in the segregation of ores which is derived from emanation 

 of original magmas and from other sources. 



Third. The heat of the igneous rocks may render the solutions vastly 

 more active in segregating the metals from the intruded rocks. The amaz- 

 ing increase in the power of solutions to dissolve material in consequence 

 of rise of temperature has been emphasized (pp. 79-81). The meteoric 

 solutions adjacent to the igneous rocks must be at a much higher tempera- 

 ture than normal; therefore their activity is increased many fold. It 

 follows that where the solutions in sedimentary, metamorphic, or ancient 

 igneous rocks may not be sufficiently active to segregate the ores even 

 where the metal exists in sufficient quantity, they may so gain in their 

 segregating power in consequence of igneous intrusions that ore deposits 



