180 PROCEEDINGS OF THE CORDILLERAN SECTION 



At 4.45 the session adjourned, to meet at Stanford University, August 

 4, at 10 a. m. 



Session of Wednesday, August 4 



This session was held at Stanford University. At 10 a. m. the meeting 

 was called to order by Chairman C. F. Tolman, Jr. Dr. A. C. Lawson 

 was called to the chair and the following papers were read : 



SOME CHEMICAL FACTORS AFFECTING SECONDARY SULPHIDE ORE 



ENRICHMENT 



BY S. W. YOUNG 



Presented in full. 



Discussion 



C. F. Tolman, Jr., called attention to the fact that H^S is a great mineraliz- 

 ing agent and not a precipitant. 



J. C. Ray stated that high temperature veins carry H2S. 



J. E. Wolf commended the work of Tolman and Young indicating that past 

 work in sulphides should be revised. 



ROLE OF COLLOIDAL MIGRATION IN ORE DEPOSITS 

 BY JOHN D. CLARKE 



Presented in full extemporaneously. 



Discussion 



Dr. Lawson challenged the statement that alkaline solutions come from 

 magmas. 



Dr. Bastin suggested that silica may play a part, bearing minerals in 

 colloidal state. 



SOME EXAMPLES OF PROGRESSIVE CHANGES IN THE MINERAL COMPOSITION 



OF COPPER ORES 



BY C. F. TOLMAN, JR. 



Presented in full extemporaneously. 



Discussion 



A. C. Lawson questioned the propriety of too definite conclusions being 

 drawn on interpretations of rock sections. 



At 12.30 p. m. the session adjourned for luncheon, to convene after 

 meeting of the Paleontological Society. 



The afternoon session was called to order by Chairman C. F. Tolman, 

 Jr., at 4.30 p. m. and the following paper was read : 



