﻿490 ME. J. A. THOMSOIf ON THE HOENBLENDIC [Nov. I908, 



The high percentage of lime shows that the absorbed material 

 came from the zoisite-amphibolite rather than from the peridotite. 

 The abnormality of the composition, compared with that of a 

 normal igneous rock having the same silica-percentage, consists in 

 the high value for lime and the low value in alkalies. Such an 

 abnormality is, as Mr. Harker has pointed out, to be expected in a 

 mixed igneous rock.^ His other conclusion, however, that mixed 

 rocks are of nearly the same age, siuce absorption only goes on 

 when the earlier-formed rock is still hot, does not seem to be borne 

 out in this case. The occurrence of zoisite-xenocrysts shows that 

 the picrite was altered to a rock resembling a crystalline schist in 

 composition, before absorption took place. 



The mixed igneous rocks which have attracted the most general 

 attention are those of Skye and Carlingford, where in each case a 

 granophyre has invaded a gabbro of nearly the same age. Eut, 

 since the majority of basic igDcous rocks are represented by am- 

 phibolites in the crystalline schists, and since the latter were formed 

 in the deeper levels of the crust where invasions of granite are 

 abundant, one would expect that rocks formed by the admixture of 

 amphibolite and granite would be the commoner group. A search 

 through the literature of the subject shows that they are common. 

 Dr. C. Callaway has described the absorption of dark diorite by 

 granite in the Malverns.^ Prof. G. A. J. Cole has described many 

 cases of interaction of granite and amphibolite in Donegal, giving 

 rise to rocks which he has compared with quartz-diorites and horn- 

 blende-granites.^ Tourmaline-bearing amphibolites are found in the 

 Tyrol * and in the Italian Alps.^ Hornblende-granulites are formed 

 on the invasion of eclogite-amphibolites by granulites in the 

 Aiguilles Eouges.^ Somewhat similar phenomena are described 

 by Prof. L. Duparc & Dr. E. Pearce from the Urals ' ; and in Finland 

 Dr. Sederholm has described absorption of many varieties of crystal- 

 line schists on a large scale.^ These few examples serve to show the 

 widespread nature of the phenomena, and permit us to recognize 

 among mixed rocks a distinctive group formed by the 

 absorption of amphibolites by granitic magmas. 



^ ' Igneous Eock-Series & Mixed Igneous Rocks ' Journ. Geol. Chicago, 

 vol. viii (1900) p. 389. 



'^ Quart. Journ. Geol. Soc. vol. xlv (1889) p. 496. 



^ Proc. Roy. Irish Acad. vol. xxv (1905) sect. B, pp. 119 et segq. 



* B. Lindemann, ' Petrographische Studien in der Umgebung von Sterzing 

 in Tirol' Neues Jabrb. Beilage-Band xxii (1906) p. 536. 



^ W. Salomon, ' Ueber Alter, Lagerungsform & Entstehungsart der peri- 

 adriatischen granitisch-kornigen Massen ' Tscherm. Min. & Petr. Mittheil. n. s. 

 vol. xvii (1897) p. 274. 



6 E. Joukowsky, ' Su les ficlogites des Aiguilles Rouges ' Arch, des Sc. Phys. 

 & Nat. Geneve, vol. liv (1902) pp. 151-71 & 261-81. 



"^ ' Recbercbes geologiques & petrographiques sur I'Oural du Nord ' M^m. 

 Soc. Phjs. & Hist. Nat. Geneve, vol. xxxiv (1905) p. 484. 



** ' Ueber eine arehaische Sedimentformation ini siidwestlichen Finland ' 

 Rull. Comin. Geol. Finlande, no. 6 (1899). 



