90 Reviews — Geological Survey of Scotland — Geology of Coival. 



the bedded basalts of Tertiary age." The very conspicuous east-and- 

 west dykes at Ardlamont Point are not crossed by any running north 

 and south ; but, since these are regarded as continuations of the two 

 large dykes crossing the island of Bute, where one of them is 

 clearly cut by later Tertiary dykes, we may infer that the Ardlamont 

 dykes are of earlier date than the Tertiary period. Similar con- 

 clusions result from the detailed examination of other districts. 

 Within this area only five intrusions have been recognized as trachj'^te: 

 these are all dykes, which are considered to be later than the basalts. 



Three chapters are devoted to the general geological structure of 

 particular districts, and the numerous sections given in the text are 

 of great service to the readers in this connection. The structure 

 of the country about Lochgoilhead, for instance, is particularly 

 interesting on account of its proximity to the anticline. Moreover, 

 since the much frequented coach-road through Hell's Glen travei'ses 

 this region, it enjoys the advantage of being easily accessible. 



Two chapters, illustrated by a special map (Clough), are devoted to 

 Glacial deposits. The following features are indicated in the map : — 

 (1) Landslips ; (2) marine and fresh-water alluvia and peat in basin- 

 shaped hollows ; (3) boulder-clay and sandy drift without definite 

 moraine shapes ; (4) drift with well-defined moraines. The 

 direction of the stri^ ranges from S.W. through S. to S.E., with 

 few exceptions. 



The remaining chapters deal with such subjects as marine and 

 fresh-water alluvia, peat, landslips, blown sand, prehistoric remains, 

 geological aspects of the scenery, and economic resources. 



In the appendix Mr. Teall makes some general remarks on the 

 petrography of the district. After insisting on the well-known fact 

 that, in a complex series of stratified deposits, the coarser-grained 

 sediments retain traces of their original character long after all such 

 traces have disappeared from the finer-grained deposits, he proceeds 

 to illustrate the point with reference to the gneissose grits (the 

 schistose grits and greywackes of the Memoir) so lai'gely developed 

 in the Southern Highlands. Although distinctly gneissose in 

 structure and composition, they differ markedly from igneous 

 gneisses in their relation to the other rocks with which they are 

 associated, and frequently contain relics of original grains of quartz, 

 often bluish in colour, and felspar. The rocks of this class are 

 crystalline schists essentially composed of quartz, felspar, and one 

 or two micas : they are therefore gneisses in the usual sense of the 

 term. "Where conspicuous traces of their clastic origin remain they 

 may be termed gneissose grits ; when all, or nearly all, such traces 

 have disappeared they may be termed granulitic gneisses : they pass 

 by insensible gradations into felspathic mica schists. 



Plates i to V are reproductions of photographs of Natural Rock 

 Exposures, taken by Mr. R. Lunn. The Geological Survey of Scotland 

 is to be congratulated on these most effective pictures of contortion, 

 which are at once instructive and picturesque. The other plates are 

 likewise very good of their kind, and the volume generally may be 

 deemed a most satisfactory contribution to geological literature. 



