86 Reviews — Crystallization-Differentiation. 



With durain the insoluble residue is larger and coarser and the 

 solution lighter, while fusain is hardly dissolved at all, and a large 

 fibrous residue is obtained. 



In thin sections, also, a graduating change of appearances is 

 noticed ; fusain generally is composed of a mass of black and opaque 

 woody tissue with thickened cell walls and empty cell lumina. 

 Durain consists of a black, opaque, granular groundmass enclosing 

 yellow spore coats. Clarain is clear, coloured red and yellow, and 

 abounds with jDlant structures of all kinds, while vitrain is also 

 yellow and translucent, but without any trace of organic structure. 



The paper is illustrated by two plates, one in colours, showing 

 very clearly the difference in the thin sections of the four sub- 

 divisions, and in the solutions obtained from them, and also by 

 a text-figure in which their distribution in typical sections of coal 

 is shown by conventional stippling. 



W. H. W. 



Ceystallization - Differentiation in Igneous Magmas. By 

 N. L. BowEN. Journal of Geology, vol. xxvii, 1919, pp. 393- 

 430. 



I) EADEES of Anatole France's La Rotisserie de la Reine Pklauque 

 \ will remember that M. d'Astarac, having once conceived the 

 notion that sylphs and salamanders have a j^resent-day existence, 

 found no difficulty in exj^laining quite ordinary haj)penings in the 

 light of his extraordinary conception. Similarly, though happily his 

 notion rests on foundations more secure than did M. d'Astarac's, 

 Dr. Bowen has no difficulty in explaining all j)etrological happenings 

 in the light of his crystallization-differentiation conception. In 

 both cases one can observe the same wholehearted devotion to 

 a charming conception, but also the same neglect of the more 

 obvious deductions. 



Dr. Bowen criticizes Daly's views on syntexis and maintains that 

 assimilation plays but a minor part in differentiation, for, even 

 though complete abyssal assimilation be admitted, the problem of 

 the splitting of the resultant syntectic magma is still one of 

 separation of phases. He also combats the limestone-syntectic 

 hypothesis of the origin of the alkaline rocks. 



In dealing with liquid immiscibility in differentiation. Dr. Bowen 

 considers that this factor is of no importance whatever. He 

 deduces that a blotchy or patchy separation of phases must follow 

 from liquid immiscibility, and from the general absence of this 

 patchiness in natural igneous rocks he concludes that this factor is 

 not operative. In opposition to this conclusion one must point out 

 that the common occurrence of patchy differentiation in quartz- 

 dolerite sills in Scotland has led to the view that liquid immiscibility 

 may sometimes be a most important factor (Glasgow Memoir, p. 148). 



