228 Reviews — A. Harker' s Bala Volcanic Series. 



Bagshot Beds of Alum Bay has been contributed by Mr. J. Starkie 

 Gardner, who thus revises the work done previously by Dr. P. De la 

 Harpe and Mr. J. W. Salter. 



The superficial deposits are now described much more fully than 

 previously. They include the Angular Flint Gravel of the Chalk 

 Downs, which is in part a sort of " Clay-with-flints," without much 

 clay, representing the insoluble residue of a great thickness of 

 Upper Chalk. It contains also flint-pebbles, grains of quartz, and 

 other rocks. There are also Plateau Gravels, probably of Glacial 

 age ; and Valley Gravels and Brick-earth of later Pleistocene age, 

 that yield remains of Mammoth, Rhinoceros, and Palaeolithic Imple- 

 ments. Recent deposits of Alluvium and Peat, Blown Sand, etc., 

 are duly described. 



An interesting chapter on Faults and Disturbances gives us an 

 account of the remarkable folds in the strata, and of the occurrence 

 of thrust-planes or slide-faults. The double anticline of the Isle of 

 Wight is one of a series that occurs in the south and south-east of 

 England, traversing the country in an easterly and westerly direc- 

 tion, and having a steeper inclination on the north side. It is 

 remarkable that the same features characterize the folds in the older 

 rocks of the Mendip Hills.. 



Messrs. Reid and Strahan point out that in the Isle of Wight the 

 sudden downward plunge of the beds on the north side of the 

 anticline seems to be the first stage in the formation of a thrust- 

 plane or slide-fault, and on the neighbouring coast of Dorsetshire, 

 an actual thrust-plane is seen in the Chalk, and this was described 

 and figured by Thomas Webster in 1811 (in Englefield's Isle of 

 Wight). As pointed out, the date of the great movements may be 

 assigned approximately to the Miocene period. 



An interesting, but very brief chapter on Physical Geography, 

 deals with the origin of the leading physical features. It is shown 

 that the lines of drainage were determined by the anticlines and 

 synclines which form so marked a feature in the geology ; and that 

 while these lines have been maintained, the form of surface due to 

 the original movements has been lost. 



The subject of the separation of the island from the mainland is 

 very briefly alluded to, and we hope in a third edition, it may 

 receive due attention, when some reference may also be made to 

 the remarks of the Rev. W. Fox and of Dr. John Evans on this 

 interesting topic. 



The final chapter deals with the Economic Products ; and the 

 Appendices include Tables of Fossils, Accounts of Wells Sections, 

 and Bibliography. 



II. — The Bala Volcanic Series of Caernarvonshire and 

 Associated Rocks. Being the Sedgwick Prize Essay for 

 1888. By Alfred Harker, M.A., F.G.S. (Cambridge University 

 Press, 1889.) 



THE examiners for the Sedgwick Prize at Cambridge have done 

 good service to petrography in opening up the igneous rocks of 

 Caernarvonshire to investigation. Mr. Harker, the winner of the 



