SEGREGATION GRANITES 



/ 



ALFRED C. LANE 



Tufts College, Mass. 



The deposits of asbestus of the Eastern Townships in Canada 

 are the most exploited of the world. In 1919 $18,000,000 worth 

 or 3, 082,384 tons were mined. This means a great deal of develop- 

 ment and has given J. W. Dresser, the geologist who has for years 

 followed the region with the closest attention, a chance to make 

 observations which are of general theoretical interest. Fifteen 

 years ago^ Dresser suggested that certain granites seemed to have 

 been differentiated from the same magma from which were derived 

 the serpentines in which the veins of asbestus chrysotile occur. 

 This would tend to support Daly's idea^ that granite is a product 

 of differentiation from a basaltic substratum, hut not necessarily that 

 it is "syntedic,'' that is, due to previous assimilation of something 

 like a quartzite. 



Some twenty years ago I had occasion to study with critical 

 care what I then called "acid interstices" which practically always 

 occurred near the middle of every diabase dike of over ten meters 

 thickness or so.^ I had over two hundred thin sections, and while 

 Bayley and Irving and Wadsworth were incHned to believe the 

 interstices filled with micropegmatite were secondary, I was inclined 

 to agree with A. C. Lawson in believing them primary. By a 

 careful study I convinced myself that such was the case. Later 

 — studies showed that the fiUing of similar interstices in effusive 

 rocks was characteristically different, and I called the effusive 

 texture doleritic. The conception I gathered was that these 



^ See Bull. Geol. Soc. Am., Vol. XVII, p. 510; also Canadian Survey Memoir, 

 Vol. XXII, and other papers by Dresser given in Ferrier's finding list. 



^ Igneous Rocks and Their Origin, p. 361. 



3 Geological Survey of Michigan, Vol. VI (1899), pp. 235-42, the work was largely 

 done in 1890; see Report of the State Board of Geological Survey of Michigan for the Years 

 i8gi and i8g2, p. 177. 



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