The Mexican mining journal . mining district, are ofeconomic importance as influencing the scale of wages,these being less than in any other mining camp in thecountry. The corollary is that, other things being equal,here should be profitably mined ore of lower gradethan elsewhere in Bolivia. Nature apparently has pres-erved the balance by making the grade of ore averagebetween 2 and 3 per cent tin, which is appreciablylower than the average of the famous mines of Unciaand Llallagua near Huanuni, and other localities. Geology. The Berenguela mountain is situated in the line ofthe Cordillera Rea
The Mexican mining journal . mining district, are ofeconomic importance as influencing the scale of wages,these being less than in any other mining camp in thecountry. The corollary is that, other things being equal,here should be profitably mined ore of lower gradethan elsewhere in Bolivia. Nature apparently has pres-erved the balance by making the grade of ore averagebetween 2 and 3 per cent tin, which is appreciablylower than the average of the famous mines of Unciaand Llallagua near Huanuni, and other localities. Geology. The Berenguela mountain is situated in the line ofthe Cordillera Real or eastern range of the Andes. Themain direction of this range is northwest. Parallel withthis range and west of it we have the Cordillera Occid-ental, with many volcanoes, the probability being thatthe upheaval of the Cordillera Real caused a line ofweakness here, this being indirectly the cause also ofthe western range being formed subsequantly. * From The Mining Magazine. February, 1915. THE áUiiX CAN MINING JOURNAL 54. Tin mine, Oruro, where the tin occurs in iron and mica. In a country such as Bolivia, to which as yet geolo-gists have given but scant attention, it is necessaryto deal in generalities. As regards Berenguela moun-tain, it is formed of alternating beds of shale separatedbv quartzite and sandstone. In places, in order to dis-tinguish between quartzite and sandstone, it would h¿necessary to make a microscopic examination. Someof the slate on the west side of the mountain occasion-ally yields round balls, which, on fracturing, discloseimpressions of bivalves and other shells. M»Te fossils have not yet been found to enablethe geologic age of these rocks to be determined. Fos-sil impressions are common on both sides of Beren-guela mountain. On the west side of the mountainthese alternating beds have been tilted, and in the mainhave now a strike northwest, dipping 30° northeast. The principal lodes on this side cut the formationapproximately
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