Whittlesey's tiieokv ok segregation 321 



|)reheiisioii ol' the "iiK^taniorphisiii/' oL' wliicli Jie spoke, his elaiiii that the 

 iron ores of Lake Superior are the result of segregation, under some 

 widespread impulse, contains the germ of one of the processes which have 

 proved to have been concerned in the production of the great ore masses. 

 This trio of nature in the production of these ore masses may be stated: 



p]ruptioii, Whitney. 

 Sedimentation, Whitney. 

 Segregation, Whittlesey. 



The error has been that geologists have restricted their view, and often 

 have presented one only of these processes as adequate to produce the 

 results, and have extended their hypotheses over ore bodies, which are 

 utterly repugnant to their initial ideas. 



Whitney, for instance, when dwelling on the eruptive origin, trans- 

 gressed chemical laws and the natural affinity of the elements; and, when 

 representing the sedimentary theory, had to ignore some of the structural 

 complexities. Whittlesey^s idea, broadly embraced by him under the 

 term nietaniorphisin, as then understood, involved transpositions of mat- 

 ter in the rocks which are not known to have been caused by metamor- 

 phism;. but that was due, let us believe, to the then miscomprehension, 

 or vagueness, of the term. His germinal thought was segregation, and 

 that has subsisted and has been found essential to a correct understand- 

 ing of the history of the Lake Superior ores. Whitney never entertained, 

 so far as observed by the writer, the theory of segregation, nor did any of 

 those who followed in his track when he urged the eruptive hypothesis. 

 His sedimentary hypothesis, however, has had numerous modifications, 

 sometimes chemical and sometimes mechanical, and when chemical they 

 have verged toward segregation, at least toward alteration. The most 

 im])ortant of these suggested modifications is that of J. P. Kimball, who 

 applied il, in the ilrsi instance, to the iron ores of Cuba,^^' but later ex- 

 tended it in part to the ores of Lake Superior. Thus he states clearly 

 that "the large bodies of specular oxitle, together with other associated 

 ferruginous aggregates (in part of magnetic oxide), are secondary ])rod- 

 ucts from the decomposition of basic eruptive rocks," and "the other 

 great bodies of ferric oxide in North America, like the Huron ian deposits 

 of Michigan and Wisconsin, are similarly derived from the decomposition 

 of highly but less basic rocks of nietaniorpJiic and not of direct eruptive 

 origin. Such stratified specular iron ore bodies are believed to owe their 

 existence to the accumulation, by precipitation, of ferric oxide from 

 basins of water receiving their drainage from such basic rocks." How- 

 ever far this be from AVhittlesey's idea of "metamorphism," or from the 



10 American Institute of Mining Engineers, vol. xiii, 



