Reviews — Geology of Ben Nevis. 31 



consequently diminishes the complexity of structure. Without 

 special knowledge of the area it is impossible to decide between the 

 rival views. Mr. Bailey, however, accepts Mr. Carruthers' interpre- 

 tation as on an equal footing with his own for the district in question, 

 his own view being based on a restricted sequence and greater 

 structural complexity. 



The interest of the region is well maintained in the next series of 

 rocks, the Old Red Sandstone lavas which centre about Glen Coe and 

 Ben Nevis. They consist of hornblende-, pyroxene-, and biotite- 

 andesites, with rhyolites, and have been poured out on to a very 

 uneven surface of the Highland schists. The two great areas of lava 

 in this region, although forming the highest ground, owe their 

 preservation to subsidence within great circular faults. One of these 

 encircles the Glen Coe lavas, except on the south, where the fault- 

 line is broken through by the Cruachan granite. Igneous material 

 rose along the peripheral fault during subsidence, but never penetrated 

 to the inner side of the fault plane. The fault intrusion is chilled 

 against the fault plane, and is usually separated from it by a band of 

 flinty crush-rock produced by the friction of the subsiding mass. 



Both the larger granite masses of the region show distinct inner 

 and outer portions, of which the former are the younger. They are 

 interpreted as magmas which filled the voids caused by successive 

 cauldron-subsidences. The concentric arrangement of the Ben Nevis 

 granites and lavas is explained in this way. The magmas are 

 believed to have been emplaced largely by the stoping method 

 described by Daly. 



The detailed petrography of the Old Bed Sandstone igneous rocks is 

 dealt with in a separate chapter. Their composition is illustrated 

 by a fine series of new chemical analyses. There is a useful 

 historical account of the terms granite, granitite, tonalite, adamellite, 

 banatite, granodiorite, etc., but the conclusions adopted as to their 

 scope are open to criticism. Two new rock names, aplogranite and 

 appinite, have been invented, but their definitions are at once too 

 vague and broad to be of much use. The uselessness of measuring 

 the quantitative relations of the minerals of igneous rocks by the 

 recognized micrometric methods is illustrated by a highly fallacious 

 diagram. 



The various granites of the region have produced remarkable 

 metamorphic effects on a great variety of rocks, including schists, 

 sediments, and igneous rocks. These are dealt with in a chapter 

 which is a distinct contribution to the literature of contact 

 metamorphism. 



A group of W.N.W. dykes of dolerite, basalt, and monchiquite are 

 regarded as of Tertiary age. A small explosion vent in the Allt 

 Coire na Ba may also be Tertiary. The breccia is invaded by a basic 

 rock which proves to be a fresh nepheline-basalt. 



The final chapters deal with the glacial phenomena and with the 

 economic products of the area. Boofing slates and granite are 

 quarried on a comparatively large scale at Ballachulish. 



The memoir, which has been edited and mainly written by 

 Lieut. E. B. Bailey, is excellently illustrated by twelve fine plates 



