ADIRONDACK MAGNETIC IRON ORES 165 



peaks of which the highest is a little over iooo feet. The approach 

 from the western side where it falls toward the Bouquet river is 

 more gradual. 



The mine openings are in the face of a cliff fronting directly on 

 the lake just north of the little cove that is locally known as Snake 

 Den harbor. They lie about ioo feet above the shore and consist 

 of two drifts, 10 feet or so wide, which follow the ore back into the 

 mountain for a short distance. The workings date back over 25 

 years, as Smock states in his report that no ore had been mined 

 for six years previous to his visit. The concentrating works, 

 erected on the lake shore below the mine, have fallen into decay or 

 have been removed. A magnetic process was employed for sepa- 

 rating the magnetite from the gangue. 



The main mass of Split Rock mountain consists of light gray 

 anorthosite, with local intrusions of gabbro. Both rocks show 

 strong crushing effects, the former in the granulation of the labra- 

 dorite which constitutes almost the entire mass, and the latter 

 in its markedly gneissoid texture as well as a similar granulation 

 of its constituents. Both contain secondary garnet. The gabbro 

 in thin section is seen to be mainly composed of augite, hypersthene, 

 brown hornblende, garnet and labradorite, with olivine and magne- 

 tite in subordinate amount. The hornblende is plainly a result 

 of chemical reaction between the magnetite and the feldspar 

 brought about by the dynamic metamorphism which the rock has 

 undergone. An analysis of the gabbro quoted from the paper 

 by Professor Kemp is given on page 148 of this report. 



The deposits occur directly in gabbro of which there is a consid- 

 erable area in the vicinity. The relation between the ore and wall 

 rock is that of complete gradation, there being no line of demarca- 

 tion whatever between the one and the other. The magnetite in 

 the gabbro increases in proportion until it becomes the principal 

 constituent; while there is a corresponding retreat of the silicates, 

 the feldspar being the first to disappear. A peculiar feature re- 

 vealed by examining thin sections is the occurrence of veinlets of 

 magnetite that evidently are the fillings of rifts in the ore subse- 

 quent to its consolidation. The veinlets are minute, but they can 

 be traced generally across the whole section, breaking through 

 the silicate minerals as well as the inclosing magnetite. It would 

 appear that there must have been a secondary infiltration of magne- 

 tite, perhaps from a fused portion of the body at depth. Another 

 singular phenomenon, noted by Professor Kemp in the ore from 



