,8,,. SOME NEW BOOKS. 393 



The schists of the central Scottish highlands, with included quartzites 

 and limestones, and the lithologically similar rocks of Donegal, Mayo, 

 and Galway, are named Dalvadian, from Dalriada, a north Irish 

 kingdom that sent out very successful colonists into Scotland. Like 

 the American " Algonkian," this may come to be a very useful term, 

 if confined, as its author would desire, to the localities in which it has 

 originated. Sir A. Geikie, in cutting off this group from the Archaean, 

 admits that it may contain rocks of various ages, from Archaean to 

 Upper Cambrian ; " sills" of igneous rock occur on a number of 

 horizons in it, and in Co. Tyrone coarse volcanic agglomerates and 

 lavas are recorded at its base. 



Anglesey comes in for an interesting discussion ; a core of 

 Archaean gneiss is admitted " with some confidence " ; and the schists 

 are regarded as a metamorphosed clastic series, referred to the 

 Dalradian, and including the quartzite of Holyhead Mountain. The 

 important announcement is made that this latter rock is crowded 

 with annelid-pipes ; whether these are Precambrian or Lower 

 Cambrian must be left an open question. 



All through this portion of the address one sees a growing 

 tendency to assign a Precambian age to the Torridon Sandstone, 

 though this is not expressly stated ; in fact, the officers of the Geo- 

 logical Survey only proved this point a few months later. While 

 dealing with volcanic rocks, question after question of this kind has 

 confronted the author ; and the fear is that stratigraphical assertions 

 or admissions of a most important character occurring in this 

 address, may be overlooked by general workers, owing to their being 

 interwoven with details of a more petrographic nature. Let us at 

 once say that no one interested in the Precambrian controversy can 

 afford to be without the address of 1891. 



The candid acceptance of the views of critics of the older work 

 of the Geological Survey is noticeable in the treatment of successive 

 systems ; but the acceptance or rejection of such criticism has been 

 fairly based by the author on a review of the evidence in the field 

 itself. Dr. Callaway's term " Uriconian " is thus adopted for the 

 Wrekin volcanic series ; and the great eruptions of the Cader Idris 

 area are believed to have broken out in Tremadoc times, attaining 

 their great development in the Arenig. The suggestion of a basal 

 volcanic agglomerate in the quartzites and shales of Howth has 

 already called forth a rejoinder from Professor Sollas, read recently 

 before the Royal Dublin Society. 



The second address, delivered in February, 1892, opens with an 

 extensive account of the Old Red Sandstone volcanoes. Trachytes 

 are recorded from near Jedburgh ; and still more t3^pical examples 

 are described later, with analyses, from the Lower Carboniferous of 

 the Garlton Hills, the rock of Traprain Law being regarded by 

 Dr. Hatch as a phonolite. Interest attaches to the volcanic necks in 

 the S.W. of Scotland which traverse the Coal-measures ; others are 

 correlated with these, and a Permian volcanic series is established. 

 As already mentioned, the andesites in the red rocks of N.E. Devon 

 are removed, somewhat conjecturally, from the Trias back into the 

 Permian. 



The Tertiary volcanoes are dealt with more summarily, owing to 

 the author's important paper on this subject in the Tvansactions of the 

 Royal Society of Edinburgh (1888). He maintains that the more acid 

 rocks of Skye and Mull are intrusive both in the basalt plateaus and 

 the gabbros, which have been usually regarded as the later series ; 



