PAPERS PRESENTED AT GENERAL SESSIONS 27 



STUDYING MIXES WITH A MICROSCOPE 



W. S. Bayley, University of Illinois 



(Abstract) 



The address by President Bayley was on the modern 

 methods of studying mines with the microscope to deter- 

 mine the way in which their ores have been formed, and 

 thereby to learn something as to their expectancy of life. 

 The lantern pictures of extremely thin sections of rocks, 

 disclosing the minerals composing them, were graphic 

 and beautiful. 



The speaker introduced his subject by explaining 

 briefly how pieces of rock are ground so thin that they 

 are transparent, and how in these transparent sections 

 the character of the different minerals present and their 

 relations to one another may be discovered by allowing 

 polarized light to pass through them and noting the ef- 

 fects. Photographs of thin sections of granites, horn- 

 blende-schists and other rocks were thrown on the 

 screen and the methods by which the minerals in them 

 were recognized were explained briefly. After giving 

 a general view of the differences between some of the 

 commoner rocks and the changes that take place when 

 one type is changed into another, the speaker threw on 

 the screen a number of photographs of the ore and asso- 

 ciated rocks from some of the iron mines in North Caro- 

 lina and showed that the ore was derived from deep- 

 seated sources. It was inferred therefore that the ore 

 body was persistent downward as far as mining is profit- 

 able. Incidentally, the minute character of the ore was 

 observed and a method for concentrating it was sug- 

 gested. It was seen from the photographs that the ore 

 consists of magnetite and hornblende so inextricately 

 mixed that it is hopeless to attempt to separate them. It 

 was seen, however, that these two minerals are also mixed 

 with quartz, which is an objectionable component, but in 

 such a way that it can be separated from the magnetite 

 and hornblende by crushing and treatment with a mag- 

 net. The hornblende is not injurious to the ore and con- 

 sequently its presence in the concentrate does not in- 

 jure it. 



