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SCIENCE PROGRESS 



sediments ; but they appear to me to be altered igneous rocks, 

 and there seems no adequate reason for separating them from 

 the similar rocks that form the Archean plateau of Australia. 

 The rocks are gneiss, and mica- and hornblende-schists, and in 

 the lode are masses of garnetiferous quartzites. The rocks have 

 been traversed by powerful faults. The lode outcrops as a 

 single vertical lode, which has been worked by an open cut. 

 The lode widens below and forks ; as a rule, the north-western 

 branch is the larger and more persistent. The south-eastern 

 branch is sometimes a short, thick pocket (fig. 5, b) ; at others 

 a spur, which follows the foliation planes in places, and some- 

 times crosses them; and in some places (fig. 5, c) there is no 

 trace of the eastern branch. 



Fig. 5. — Three sections across the Broken Hill Lode near the McBryde's Shaft 



in the Proprietary Mine. 



a. Shows a thickening on a vertical lode. 



b. A saddle-shaped arch of which the eastern limb ends in a pocket. 



c. Shows no trace of the second branch of the, lode. 



The division of the lode occurs at depths of from 200 to 

 400 ft., where there is a great increase in the width of the 

 lode. In 1892, when the field was examined by Mr. E. F. 

 Pittman, the Secretary of Mines of New South Wales, the most 

 striking feature in the lode was this thickening, from which 

 two branches went downward, along the structural planes of 

 rocks. He made the very useful suggestion that the lode was 

 a saddle reef; and if that hypothesis had been substantiated, 

 similar arches in the lode might have been expected to recur 

 below. Pittman's suggestion was adopted in the valuable 

 report on the field by Jaquet, published in 1894, as one of 

 the Memoirs of the Geological Survey of New South Wales, 



