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relative age of the containing rock also determine the relative age of the 

 mineral vein ? So long as geologists believed mineral veins to have 

 been formed by sublimation from below, the answer to this question 

 must have been in the affirmative, for the deeper the fissures, the 

 nearer would be the source of the metallic sublimates. But when this 

 hypothesis was shown by the gradual progress of mineralogy, and a 

 more careful study of the question from a chemical point of view, to 

 be untenable ; and that the greater number, at all events, of mineral 

 veins have been formed by precipitation from descending solutions, 

 there was no longer any necessary connexion between the relative age of 

 the containing rock and that of the vein. The fossils found in the rocks 

 afford satisfactory evidence in most cases of their relative ages, but until 

 within the last few years no fossils had been discovered in mineral 

 deposits. In many places we find pseudomorphites of several metallic 

 ores in the form of fossils ; as at Wiesloch, in Baden, where we find 

 the limestone of the muschelkalk, which is one mass of shells, con- 

 verted into Smithsonite or zincic carbonate. Again, at Miinsterappel, in 

 Ehenish Bavaria, cinnebar is found coating fish impressions of Amblyp- 

 terus, and in small crystals in the interior of Calamites. But the inter- 

 change between the calcic and zincic carbonates in the muschelkalk, and 

 the infiltration of the mercuric solution may have taken place at any 

 time since the deposition of the rocks in which the ores are found. These 

 cases then afford no satisfactory evidence of the recent formation of 

 mineral deposits in rocks of considerable geological age. 



In a valuable paper on the Geology of Bolivia and Southern Peru, 

 read to the Geological Society of London, in November, 1860, Mr. 

 David Forbes mentions the occurrence of mammalian bones in the 

 Santa Rosa mine, belonging to the group of copper mines, known as 

 the Corocoro Mines. Professor Huxley, to whom Mr. Forbes sub- 

 mitted the portion of the bones which he succeeded in getting, 

 has shown that the animal belonged to the camel tribe, and was 

 closely related to the existing llama of the Andes. He named the 

 species Macrauchenia Boliviensis. The bones are in some instances 

 " almost converted into copper, or at least the pores are filled with that 

 metal." Fossil wood has also been found at a considerable depth at 

 the same mine. The occurrence of a post-pleiocene fossil in a mine 

 in Permian rocks would settle the relative age of the mineral deposit if 

 it occurred in the deposit itself. But at Santa Rosa this was not so. 

 In the Corocoro cupriferous formation, as we learn from Mr. Forbes, 

 the ore occurs disseminated irregularly in certain beds of sandstone 

 which are of Permian age. The bones could not have occurred in these 

 beds. Mr. Forbes suggests that the animal had fallen into a fissure and 

 been subsequently cohered up by the crumbling sandy debris of the 

 adjacent rocks which had gradually consolidated. Into this fissure 

 cupric solutions would naturally be always flowing from the action of 

 water on the ores in the beds. 



Interesting as this occurrence of bones undoubtedly i3, it does not 

 help us to determine the relative age of the metal in the sandstone, 



