176 Reviews — Boverton Hedwood — On Petroleum. 



the ice winch drained from the inland country was in mass sufficient 

 to override Criffel, and must therefore have had there a minimum 

 thickness of 2000 feet — a fact of considerable interest in connection 

 with the wide dispersal of boulders of Criffel granite. 



Raised Beaches, Caves and Cavern Deposits, Peat and Alluvium, 

 and Economic Products are duty mentioned. 



Considerable interest naturally attaches to the large granite mass 

 which covers upwards of seventy-five square miles of ground. The 

 granite and its apophyses traverse strata of Llandovery, Wenlock, 

 and Ludlow age ; but the intrusion of the igneous complex must be 

 older than the Upper Old Red Sandstone. Though mainly massive 

 in character, yet in certain limited tracts along its margin the granite 

 has a marked foliated character, and evidence is given to show that 

 this foliated structure has been produced by mechanical deformation 

 which has simultaneously affected, not only the main body of the 

 granite, but also the basic inclusions which this rock contains, as well 

 as the acid and even the quartz veins that traverse it. It is pointed 

 out that the quartz and alkali-felspar, which were the last con- 

 stituents of the granite to solidity, are those which have yielded 

 most in the deforming stresses; while the fact that the foliation in 

 the acid veins has no reference whatever to the direction which they 

 take, is stated by Mr. Teall to be a striking proof that it cannot be 

 due to fluxional movement during intrusion. 



Dykes of porphyrite occur not only in the sedimentary rocks but 

 also in the granitic masses. It is pointed out that the term 

 " porphyrite " has hitherto been employed in a different sense by 

 the Geological Survey, for certain lavas which occur in association 

 with Palaeozoic sediments, and which in reality are merely altered 

 andesites. The present usage of the term is that adopted by Prof. 

 J. P. Iddings for rocks of the type under consideration, which occur 

 as sills and laccolites as well as dykes. 



A detailed list is given of the rocks examined under the micro- 

 scope, with their localities, and with remarks on their mineral 

 structure. 



We may add that the printing by Messrs. Neill and Co. compares 

 so favourably with that noticed in a recent Survey Memoir printed 

 in England, that we wonder H.M. Stationery Office does not have 

 all its printing done in Edinburgh. 



II. — Petroleum. By Boverton Redwood, F.R.S.E., assisted by 

 Geo. T. Holloway and other contributors. Two Vols. Svo. 

 pp. 900. (London : Charles Griffin and Company, 1896.) 



THIS comprehensive treatise is in every way creditable to both 

 author and publisher : it has been prepared with care and 

 skill, printed in clear and varied type, and provided with numerous 

 illustrations. Its two volumes together comprise no fewer than 

 900 pages ; there are 327 figures in the text ; two frontispieces 

 show respectively the distribution of petroleum throughout the world, 

 and the appearance of the flame-caps corresponding to six different 



