. Annual report. New York State Museum; Science; Science. ADIRONDACK MAGNETIC IRON ORES 95 the lines of outcrop are shifted laterally. In the heading of the south shaft of the Nelson Bush mine a fault of this kind was observed. Its throw could not be determined but it is probably small. Other examples which have been noted by Emmons occur in the old workings on the southern section, where the outcropping ore is offset by slight displacements that have taken place obliquely to the dip. The maximum offset found on the surface is about 15 feet. In this case a thin dike has been intruded along the
. Annual report. New York State Museum; Science; Science. ADIRONDACK MAGNETIC IRON ORES 95 the lines of outcrop are shifted laterally. In the heading of the south shaft of the Nelson Bush mine a fault of this kind was observed. Its throw could not be determined but it is probably small. Other examples which have been noted by Emmons occur in the old workings on the southern section, where the outcropping ore is offset by slight displacements that have taken place obliquely to the dip. The maximum offset found on the surface is about 15 feet. In this case a thin dike has been intruded along the fault plane [fig. 15]. The wall rock is mainly the augite variety of acid gneiss already described. Along the contact with the ore it has been considerably altered, with the development of chlorite and biotite as resultant products from the augite, while it also contains much clear quartz of secondary infiltration. A black hornblende gneiss is encoun-. Fig. is Faulting of the ore bodies as seen on the surface near the Indian pit. A diabase dike has been intruded along the fault plane at the right. tered on the walls of the Nelson Bush mine, and may represent an included band of the sedimentary gneisses to which it corresponds in composition. Nelson Bush mine. This mine is the most northerly of the Arnold hill workings. It consists of two shafts about 600 feet apart driven on the course of two lenses which have nearly the same horizontal axis. Underground the shafts run off as inclines, the northern starting at an angle of 6o° and flattening gradually to 300 and the southern at an angle varying from 420 to 350. They are intended to follow as nearly as possible the pitch of the lenses which is about 400 north. The north shaft is down some 900 feet on the incline. The lens of ore as seen in the workings is 25 feet thick in its maximum development and averages perhaps 18 feet. In the south shaft the lens ranges from 10 to 15 feet across the walls. The two shafts are not connected
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