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BULLETIN OF THE 



only in the compact portions (lower) of the rock, but also in the scoria- 

 ceous parts (upper). These amygdules and pscudo-aniygdules are com- 

 posed of quartz, calcite, epidotc,prehnite,Iaumoutitc, analcite, apophyllite, 

 datolite, cidortte, delessite, etc., etc. The constituents of these minerals 

 were derived from the decomposition of the melaphyr, and deposited 

 through the agency of the percolating waters. The vein materials are 

 the same as those of the amygdules, and they are of like derivation and 

 deposition. The copper is found forming a constituent part o( the amyg- 

 dules in many places, as well as of the vein-stone, and it would seem to 

 have been deposited in a like manner. Until we know more about the 

 occurrence of the copper, all theories regarding its origin should be held 

 with a loose grasp, and dropped as the facts developed may require 

 thereafter. It is held by some that the copper was derived from solu- 

 tions of the metal in sea-water, precipitated by decaying organic matter, 

 and accumulated in the sandstones, shales, and conglomerates of the 

 series. It was then taken up by the percolating waters, and deposited 

 in the places in which it is now found. A second view is that the cop- 

 per was originally finely disseminated through the lava at the time of its 

 outflow, and has since been locally concentrated by percolating waters 

 in the amygdules, veins, and conglomerate beds. The writer inclines to 



the latter view, believing that this theory is more in accordance with 

 the facts observed by him than the former one. The final concentra- 

 tion and precipitation seem to be connected in some way with the ox- 

 ides of iron, which are abundant in the melaphyr and in the detritus of 

 it and of the felsite pebbles, which form the principal portion of the con- 

 glomerate. The copper seems to have needed for its deposition some of 

 the following conditions: rocks that were porous and cellular; those 

 whose parts were easily removed by the percolating waters, as the mud 

 forming the cementing material of the conglomerates; the open spaces of 

 veins and fissures ; and rocks acted upon by hot waters. TIxq coj)per, 

 when not distributed through the whole bed, is found principally in the 

 upper portion. Whatever may be our views respecting the sources of 

 the copper, it is evident that it was deposited by aqueous agencies, and 

 that the general course of the solution was downwards. The best vein- 

 stones, so far as observed, are datolite, prehnite, and caleite. Laumon- 

 tite does not seem to have much mass copper associated with it. While 

 large masses of copper were seen at the Central mine associated with 

 caleite, a similar association is I'arely found in the Owl Creek vein at 

 Copper Falls. The best vein-stone there has been datolite. The preh- 

 nite here seems in depth to yield to datolite. 





