90 PROCEEDINGS OF THE PRI^'CETON MEETING 



The Hudson gorge in the vicinity of New York : 

 The Pennsylvania tunnel profile. 

 Correlation of the bedrock channels. 

 Confirmation of the deep Pleistocene channel. 



Nature of the bedrock floor of the Hudson south of tbe Highlands. 

 Possible bearing of differential elevation. 



Presented by title. 

 The section adjourned 



ABSTRACTS OF PAPERS PRESENTED BEFORE THE THDID SECTION AND 

 DISCUSSION THEREON 



The third section met at 2.40 o'clock p. hl, with Vice-President James 

 F. Kemp in the chair and F. E. Van Horn acting as secretar)\ 



COMPOSJTIOy OF BORXITE AXD ITS RELATION TO OTHER SULFOMIXBRALS 



BY EDWABD H. KBATJS 



iAl)stract) 



As the result of a new analysis of exceptionally well crystallized bomite and 

 a study of the published analyses of the mineral, the composition of bomite 

 is shown to vary considerably. It is, however, possible to establish a definite 

 series extending from chalcopyrite to chalcocite. the minerals of the series 

 conforming to one general formula. This general formula seems also to 

 underlie the composition of practically all the minerals, which are usually 

 interpreted as sulfoferrites, arsenites, etcetera. 



Presented in abstract without notes. 



Discussion 



I>r. J. E. PoGtx pointed out the importance of metallographic examination 

 of sulphide minerals subjected to analysis because of the prevalence of inter- 

 grown microscopic impurities. Such examination needs also to be undertaken 

 under high magnific-ation. for impurities not visible at magnifications of, say, 

 X 40 appear at X 2(X). The divergence of older bomite analyses may be due 

 4u part to microsc-opic impurities. The bomite formulas of Professor Kraus, 

 showing increasing copr>er content, suggest the relation of the principal copper 

 minerals of the Mount Lyell Mine. Tasmania, which, in the order of their 

 formation, are cupriferous pyrite. chalcopyrite. bomite. and chalcocite — an 

 order corresponding to decreasing iron and increasing copper content. 



Prof. J. y. Lewis said that all teachers of mineralogy would be indebted 

 to Doctor Kraus if some simple arrangement in the formulae of complex sulpho- 

 salts, such as suggested by Doctor Kraus, could be proveiL 



