172 



crystal was an obtuse rliomboid, and tliat its plane seemed to corre- 

 spond with the natural faces of the calc-spar in which it was im- 

 bedded. 



Mr. Marcou made some remarks on the occurrence of 

 silver and gold in the Rocky Momitains and California. 



According to his own and others' observations, all the gold mines 

 are in the chains running north and south, as the Sierra Nevada, 

 which is separated from the Rocky Mountains, and older than they 

 are. Gold Mountain is near Santa Fe, where the mountain chain is in- 

 terrupted. In the Sierra Madre, running north and south in Arizona 

 and Sonora, gold is also found ; he was of opinion that Pike's Peak 

 must be out of the true line of the Rocky Mountains, and an isolated 

 part of a north and south chain. Silver, on the other hand, is found 

 in the chains running northwest and southeast, as the Sierra Cerbal, 

 farther to the east, and in a chain having the same direction in 

 Arizona and Sonora. 



In reply to a question, if gold is not usually found with pyrites, 

 Dr. Jackson said that gold generally occurs in metamorphic micaceous 

 or argillaceous slates, and that in auriferous rocks the pj^ites almost 

 always contain gold; in the Southern States the pyrites do not 

 contain it, but the hematite of North Carolina and Georgia does. 



Mr. Marcou observed that the gold region of California has the 

 outward reddish appearance of an iron district. 



Professor W. B. Rogers stated that in the auriferous region of 

 Virf^inia and the CaroUnas, there is a large mechanical mixture of 

 the gold with sulphuret of iron. As an instance of the extent to 

 which this is decomposed, he said that he had often found the interior 

 of cubical cavities, formerly filled with pyrites, containing pure crys- 

 tallized sulphur. 



Dr. Hayes was of opinion that the gold was originally mineralized 

 with pyrites, and that its separation has been the result of chemical 

 and electrical actions, the oxidation of the iron going on, but not that 

 of the sulphur. 



Dr. Jackson stated that there had been much discussion as to 

 whether the gold was mechanically or chemically mixed with the 

 pyrites ; in common with many practical miners, he believed that it 

 is mechanically mixed. 



Dr. Hayes said that in common with most chemists, so far as he 

 knew, he considered the gold as chemically mixed with the sulphuret 

 of iron. 



Professor Rogers thought it would be extremely difficult, if not im- 

 possible, to decide the question positively, as in the last degree of 

 attenuation practicable, all the time yielding gold by amalgamation 

 with quicksilver, the quantities are so small as to defy chemical 

 appreciation. 



