228 KANSAS CI TV RE VIE 1^1^ OF SCIENCE. 



material mixed with or holding the ore, consists of hydrated iron oxides or man- 

 ganese oxides, silica and clay, all secondary products, the clay coming from the 

 decomposed porphyry. The cavities in the Hmestone were made by the eroding 

 solutions which introduce the ores ; the action commenced at the top of the lime- 

 stone adjoining the sheet of porphyry, and from this plane worked downward 

 into the limestone. The materials of the ores were taken from " circulating 

 waters, which, in their passage through the various bodies of eruptive rocks, took 

 up certain metals in solution, and, concentrating; along bedding planes, by a 

 metaraorphic or pseudomorphic action ot replacement, deposited these metals as 

 sulphides along the contact or upper surface, and to greater or less depth below 

 that surface, of beds generally of limestone or dolomite but sometimes also of 

 siliceous rocks." Dikes intersecting the ore-bearing formation "seem to favor 

 the concentration of rich ore-bodies or bonanzas in their vicmity ; " but the planes 

 of faults afford no deposits of importance, and evidently for the reason that 

 "their origin is later than that of the original ore-deposits." Thus the intrusion 

 of the igneous sheets preceded the production of the ore-deposits and of the cavi- 

 ties containing them; and the production of the ores antedated the era of great 

 disturbance which closed the Lignitic period or the Cretaceous, and which has 

 continued to be followed by feeble movements until the present time, even since 

 the opening, according to some evidence, of the Leadvilie mines. 



These ores occur, according to the same authority, underneath a pori^.hyry 

 sheet and chiefly in cavities penetrating the lowest member of the carboniferous 

 formation, the blue limestone— but occasionally also underneath the same porphy- 

 ry in the white or silurian limestone and the Cambrian quartzite. The ore de- 

 posits penetrate into the limestone to varying depths from its plane of contact 

 with the overlying ignec.us rock, sometimes following courses of natural joints (ir 

 cleavage planes. 



The product of the Leadvilie mines for the past six months has been about 

 $7,815,000, which if kept up for the whole year will exceed that for i88r. Even 

 this showing would be larger had it not been for the burning of the Grant smeller 

 in June, which necessitated the sending of large quantities of ore to Pueblo and 

 Denver, the returns for which had not been received when the above statement 

 was given out. 



The mines over the Range in Pitkin County are being actively worked and 

 the prospect is that the Farwell Company at Independence will find abundant 

 work for both stamp mills from their own mines, as they are driving the Dicker- 

 man Tunnel with all the men they can work, are also developing the Mt. Hope 

 Mine and have their larger mill full of ore now; while those of Ide, the Hamilton 

 Company and others promise well. The last named company are not at work on 

 theirs at present, but are securing patents to their placer and lode claims, after 

 which they propose to resume active operations. C. 



