THE llEPUBLIG TKOUGH. 549 



of which is in many cases miquestionably detrital. Where the quartzose 

 pebbles, from the conditions of sedimentation, happen to be few and small, 

 or where they have been removed by subsequent chang-es, the conglomerate 

 may contain enough iron to constitute a valuable ore. No large deposits 

 of this character have been demonstrated to exist in the Republic area, but 

 some good examples on a small scale may be seen about Republic Moixn- 

 tain. Such ores are usually magnetic. It is believed that a considerable 

 part of the magnetite deposits of the Champion mine belong to this class. 

 In the Republic area, around the borders of the magnetite deposits, where 

 they become too lean to mine, occur certain peculiar rocks, mixtures of 

 clear quartz and magnetite, which are usually known as "black-ore jasper." 

 Higher in the lower quartzite, thin, regularly bedded Ijands of magnetite 

 and quartz occur, Avhich occasionally rise high enough in iron to become 

 ores. They ai'e found usually a short distance above the transgression 

 plane, and are separated from it by a small thickness of quartzite. 



In certain cases the line of contact between the upper and lower series 

 may be traced directly through an ore body, which thus belongs partly in 

 one series and partly in the other. Excellent examples may be seen at the 

 Kloman oj^en pits, nortli of Republic Mountain. 



RELATIONS OP THE ORE DEPOSITS TO THE GEOLOGICAL STRUCTURE. 



In the Republic area the only deposits that have had a commercial 

 value have been found in the immediate vicinity of the southeast end of 

 the fold. The largest single body occurs at the southeast point of the horse- 

 shoe, in the easternmost of the three main subordinate synclines already 

 mentioned. The middle, or Morgan-Pascoe-Ely syncline, is the locus of a 

 great number of smaller deposits. Several deposits occur also on the 

 straight northeastern side of the trough, within three-quarters of a mile from 

 the horseshoe; but in going north along this stretcli the bodies become 

 smaller and farther aj)art, and north of the Kloman practically disappear. 

 A veiy close relation is thus indicated between the occurrence of the iron 

 ore in large deposits and tiie main structural featui'es of the trougli. 



These larger bodies are both magnetite and si)ecular hematite or slate 

 ore. (PI. XXXIV, fig. 1.) The magnetite bodies always occur immediately 



