OBIGIN AND DEVELOPMENT OE OKE-DEPOSITS. 361 



rocks such, as granite, felsite, and diabase, containing (a) 

 metalliferous silicates or (b) metalliferous sulphides, which 

 subsequently are carried off by percolating waters and deposited 

 where we find them.f It seems to me this hypothesis will 

 meet all the facts as we know them. 



Thus the phenomena of "congenial" and "uncongenial" 

 strata as observed by the miners in the West of England, and 

 the different enrichment of the lead veins in the North of 

 England as they cut through successive and alternating strata of 

 limestone grit and shale, as set forth by Wallace in 1861, 

 agreeing as they do with the most literal interpretation of the 

 lateral secretion hypothesis, agree equally well with the idea that 

 the fissures are fed by ascending metalliferous thermals. For, 

 we may readily and fairly suppose that, the circulating solution 

 being the same and complex, certain rocks have greater, or at 

 least different, precipitating capacities than others, or that some 

 supply better cavities than others. 



The following conclusions seem fairly deducible from what 

 has been here put forward. 



1. That as a rational "lateral segregation" hypothesis 

 accepts and includes " descension," so a rational "ascension 

 hypothesis " must accept and include both lateral segregation 

 and descension, and that all three have operated powerfully and 

 and extensively in the production of the ore-deposits of the 

 West of England. 



2. That sublimation has acted effectively in ore-deposition, 

 and especially as regards the elements sulphur and arsenic. 



3. That injection has also been powerfully effective, but 

 chiefly by bringing up ore-charged rocks from what may be 

 called the zone of vapour to the zone of subterranean circulation. 



f It is of course admitted that many comparatively modern stratified rocks 

 contain metallic compounds, and there is great reason to believe these in many 

 instances to have been present in some form when the strata were first laid 

 down, the substances in question having been present in the waters. But these 

 waters must have received such components in the first instance from mineral 

 springs rising from the earth, except such portions as, it may be argued, were 

 originally condensed into the first waters from the first atmosphere. 



