RECORDS. 189 



ting the andesite of the laccolith. Among these are found anal- 

 cite-tinguaites and camptonites, as well as vogesite and diabase. 

 Two main streams now drain the hollow formed by the down- 

 cutting of the dome where the weaker andesite has been laid 

 bare as far as the limestone cover has been cut back. 



Dr. Finlay's paper was discussed by Professor Kemp, who 

 called attention to the interesting association of types presented 

 by the intruded rocks ; and by Dr. H. S. Washington, who 

 dwelt on the importance attaching to the additional localities 

 here and elsewhere recently reported for the peculiar dyke rocks 

 mentioned. 



In his paper Mr. Moffet said in brief: The copper mines of 

 El Cobre are located about nine miles west of the bay of Santi- 

 ago, where a series of eruptive flows, andesites and rhyolites, are 

 interbedded with fragmental rocks, agglomerates, breccias and 

 tufts. The strike of the beds is east and west, and they dip at 

 a low angle to the north. The series is cut by trap dykes and 

 by two major systems of faults, the older of which runs east 

 and west and carries with it the large ore bodies. The second 

 major system has a direction nearly north and south. Cross 

 faults cut and displace the ore bodies of the older system, and 

 carry copper, though in less amount. The copper workings of 

 the old English mining companies produced enormous quantities 

 of very rich oxidized ore which gave place in the lower levels to 

 sulphides. Much difficulty is encountered in handling the mine 

 water on account of the porous nature of the country rock. 

 At the present time the iron ore of the region is of much greater 

 commercial importance than the copper. 



In the discussion which followed, Professor Kemp spoke of 

 the great importance to the United States which the iron ore 

 deposits possessed on account of their great extent and con- 

 venient location. The ore is extremely low in phosphorus, but 

 contains some sulphur. The copper may again be of great 

 importance, strong efforts are being made at present for its 

 exploitation, 



E. O. HovEV, 



Secretary. 



Annals N. Y. Acad. Sci., XV, May, 1904 — 14. 



