Revieics — The Surcey Memoir on the Scotti><h JJplmnh. 519 



forming the terminal member of the Sc-ottisli Silurian. On this view 

 first advocated by Messrs. Brown and Henderson several years ngo, 

 many controversial difficulties disappear, the views of local amateurs 

 and the views of the Survey are harmonized, and the Scottish 

 Silurian brought into closer parallelism with the Silurian of Southern 

 Britain and elsewhere. 



In Chapter XXVI Mr. Teall furnishes us with a masterly summary 

 of his petrological researches into the characters and constitution 

 of the Galloway granites and their associated rocks, found^^d 

 mainly upon materials collected during this revision of the 

 Uplands. He shows that the three granitic masses of Criffel, 

 Loch Dee, and the Cairnsmore of Fleet present such resemblances 

 and differences as are best explained by granting that they belong 

 to the same petrological province, and in all likelihood were 

 derived from the same magma basin. In average composition the 

 Criffel mass is the most basic — being a tonalite rather than a true 

 gi'anite; the Cairnsmore mass the most acid — a biotite granite; and 

 the Loch Dee mass intermediate in character — a hornblende granite. 

 But in each mass we find rocks which are more acid and more 

 basic than the average, extreme types being represented by 

 byperites and muscovite-biotite granites ; but between the most 

 extreme types we have a continuous series of intermediate varieties. 



The curious resemblances which obtain between these Galloway 

 rocks and similar petrological types of other areas in Britain and 

 abroad, in widely separated districts, and in rocks of different 

 geological age, are pointed out, and the conclusions are drawn that 

 plutonic rocks, like minerals, are subject to paragenesis ; and that 

 in Galloway, as elsewhere, the phenomena are in accord rather 

 with the differentiation hypothesis than with that of assimilation. 



The petrological reader will follow with keen interest tlie 

 descriptions of the minuter characters of the rock masses and rock 

 varieties — the veins, the dykes, the foliated rocks, the aureoles of 

 metamorphism and their characteristic phenomena — as given by 

 Mr. Teall in this and the following chapter, and discussed in 

 brief in their relation to each other and to the unsettled problems 

 of petrological science in general. 



When we recollect that, in addition to these special chapters, the 

 volume is enriched by numerous petrological descriptions, scattereil 

 like the sketch-plans and sections through its pages, we appreciate 

 how important a role the science of petrology has now begun to 

 play in the development of the geology of every complicated region. 

 This petrological work is illustrated by several excellent micro- 

 photographs, but it is to be lamented that it is accompanied by so 

 few chemical analyses. 



The final chapter in the volume deals with the Economic 

 products of the Upland rocks — the building-stones, the granites, 

 the ornamental stones, the workable ores, etc. We consider this 

 chapter, more especially because of its brevity, as the least 

 satisfactory in the book. The economic geology, as such, is as mu(jh 

 the province of the geologist, and demands as respectful a treatment, 



