548 SCIENCE PROGRESS 



confirmation and extension of Bowen's theory of differentiation 

 by the straining off of residual hquid from a crystalUsing mass 

 {Journ. GeoL, 29, 1921, 701-19). The intrusion consists of a 

 central mass of quartz-norite surrounded by a marginal zone of 

 normal norite, in which there are smaller bodies of olivine-rich 

 types. The crystallisation of the intrusion went on under 

 directed pressure due to Caledonian folding. As crystallisation 

 proceeded inward from the margins, and the crystal mesh 

 became strong enough to take up the stress, the more acid 

 residual liquid was expressed towards the interior, thus contri- 

 buting to the formation of a quartz-rich norite in that position. 

 In Foslie's words, " the wave of crystallisation is followed by a 

 wave of squeezing." This conception makes a valuable addition 

 to Bowen's general theory, and may, in the writer's opinion, 

 throw light on the origin of schlieren in igneous rocks. 



N. L. Bowen has experimentally determined the rate of 

 diffusion in certain silicate melts by permitting diffusion against 

 gravity of a heavy liquid into a lighter one {Journ. GeoL, 29, 



1921, 295-307). The value of -25 is taken as near the aver- 

 age diffusivity in igneous magmas measured in grams passing 

 through unit area per day. On this basis it is shown that the 

 formation of border phases in igneous intrusions by diffusion 

 towards the cooling margins cannot take place in the time 

 available. It is shown, for example, that after sixty-four years 

 the precipitating effect would be felt only at a distance of 3*3 

 metres from the margin, the rest of the magma being unaffected. 

 After 256 years a layer only 8 cms. thick of the first-crystallised 

 mineral would be formed, all the material being taken from a 

 border portion less than 7 metres wide. 



In discussing the origin of the alkalic igneous rocks. Dr. J. 

 W. Evans {Report Brit, Assoc, Cardiff, 1920, p. 354) points out 

 that they occur mainly where the earth's crust is thick, the heat- 

 gradient low, and where there has been no folding since remote 

 times. Magmas under these conditions of high pressure and 

 comparatively low temperature would crystallise with the 

 formation of minerals with small molecular volumes, garnets, 

 kyanite, epidote, and zoisite, all rich in lime and alumina. 

 Hence there should be a residual magma rich in alkalies which 

 would be able to reach the surface where faulting and Assuring 

 occurred. 



An intrusion of alnoitic rocks at Isle Cadieux, near Montreal, 

 has been studied by N. L. Bowen {Amer. Journ. Sci. (v), 3, 



1922, 1-34). This rock contains monticellite (lime-olivine), 

 and it is believed to have consisted originally of augite and 

 chrysolite. With lowering of temperature these minerals were 

 attacked probably by their own interstitial liquid, and were 

 replaced by melilite, monticellite, and biotite, with marialite, 



