12 THE ROYAL SOCIETY OF CANADA 



each of the principal differentiates themselves and even in the granite, 

 showing that segregation in situ took place within the various deriva- 

 tives. It seems warrantable, therefore, to conclude that the granite 

 may have been thus segregated from magma of the peridotite phase 

 in situ in a late stage of its solidification, perhaps a stage termed by 

 Harker ^ the "squeezing of the sponge" of basic crystals, which resulted 

 in the expulsion of minor acid residues and the forming of differentiates 

 of extreme types. 



Comparison with Other Areas: Descriptions of comparable areas 

 that are applicable to this subject are not numerous in geological liter- 

 ature. An instance of differentiation of like wide range is afforded by 

 the work of Dakyns and Teall in Argyleshire, Scotland .^ Here the 

 series of differentiates is stated to include peridotite, olivine-diallage 

 (wehrlite), diorite, tonalité, and granite, the latter ranging to phases 

 of high acidity. In this series the acid rocks greatly predominate and 

 the ultra-basic rocks are of minor importance, except as indicating the 

 wide range of differentiation. In the Quebec series the rocks occur in 

 the reverse order of importance. 



In the Gowganda district of Ontario, investigated by Collins,^ 

 there is, perhaps, a better parallel. In this region the wide-spread sills 

 of Nipissing diabase contain small dykes of aplite, and masses of an 

 acid rock closely allied to aplite. Compared with the serpentine series 

 of Quebec, the Gowganda intrusives, besides being more acid in 

 composition, cooled more quickly and the differentiation is less com- 

 plete. In a summary Collins says: "Where cooling was slow enough, 

 the magma forming these large bodies (the sills) obeyed imperfectly 

 a tendency to differentiate into two parts; a principal one of ordinary 

 diabase, and a subordinate one of aplitic nature. The aplite occurs 

 as dykes and irregular segregations within the diabase." 



Elsewhere (p. 81) Collins also remarks applicably to the present 

 question, "Segregation was more or less complete according to the 

 rate of magmatic congelation .... irregular spots and patches of 

 "red rock" (a phase of aplite) from 1cm. to 100m. in diameter, and 

 aplite dykes, developed during the more protracted cooling of the sills. 

 Perhaps there was a tendency on the part of the lighter aplite to rise to 

 the upper surface of the diabase, for a considerable quantity of aplitic 

 bodies have been found in the upper portions of the sills, but the 

 results of this tendency are not strongly in evidence. 



Differentiation of diabase and aplite from one original magma 

 was accompanied by differentiation within each of these derivatives." 



^A. Harker, XH, International Geological Congress, 1913. 

 2 Cited in Geikie's Text Book of Geology, 4th éd., 1903, p. 710. 

 ^ Geological Survey fo Canada, Memoir 33, 1913, W. H. Collins. 



