568 Revieivs — Report of the Geological Survey. 



component strata, and it is noticed that in the middle of the main 

 limestone thei'e is, locally, a remarkable band of white oolite 40 feet 

 thick. The chief lithological divisions in the Millstone Grit and in 

 the Coal-measures are separately mapped, so that the structure of 

 the ground may be clearly represented. This is of great practical 

 value as regards the bands of clay-ironstone, the steam-coals, and 

 other economic products. 



Much new information has been obtained with regard to the 

 extent of the boulder drift, and to the occurrence of Esker gravels 

 in Monmouthshire and South Wales. Proof that the ice must have 

 existed in considerable bulk has been obtained in the excavations of 

 some new waterworks at Nant-y-bwch, where a hill of sandstone, 

 upwards of 200 yards long, has been found to be a transported mass. 



Some commencement has been made with the re-survey of the 

 Leicestershire coal-field by Mr. Fox- Strang ways, and of the North 

 Staffordshire coal-field by Mr. De Eance. 



It is satisfactory to learn that the results of these and other 

 re-surveys will be published on the new series of the Ordnance 

 one-inch maps, while MS. coloured copies of the six-inch maps are 

 deposited in the Geological Survey Office for public reference. 



In Devonshire and Cornwall, Mr. Ussher has been surveying the 

 subdivisions of the Devonian formation and their associated igneous 

 rocks ; while in the southern counties Messrs. Whitaker, Reid, 

 Bennett, Blake, Hawkins, and Jukes-Browne have been engaged in 

 mapping the Drifts and re-surveying the Cretaceous and Tertiary 

 rocks. The mapping of the Drifts in Yorkshire and in parts of 

 the Midland counties has been continued by Messrs. Tidderaan and 

 Cameron, who have likewise attended to needful revisions of the 

 previous survey of the older and more " solid " formations. 



In Scotland the Lewisian gneiss of the northern part of Raasay 

 was mapped by Mr. Teall. It has been determined that the various 

 crystalline rocks older than the Torridon Sandstone, and comprised 

 under the general designation of Lewisian gneiss, may be divided 

 into five distinct groups. The oldest and chief group is the 

 " fundamental complex " of banded and foliated rocks, and this is 

 considered by Mr. Teall to have decided affinities, both as regards 

 chemical and mineralogical composition, with plutonic igneous 

 products. A scheme devised by him for descriptive purposes, is 

 now published in the Director-General's Eeport. Based primarily 

 on mineralogical composition, and to a subordinate extent on 

 structure, it shows the nature of the various rocks comprised within 

 this " fundamental complex." In the other groups are included 

 various dykes, gneissose granite, and pegmatite. The observations 

 of Messrs. Peach and Home prove that in certain areas the 

 " Moine schists" have been produced by the alteration of the 

 lowest Torridonian grits and shales. 



Interesting results have been obtained by Mr. Hinxman in 

 Strathspey, and by Mr. Barrow in Deeside, with regard to the 

 relations of the great granitic masses. 



The survey of the Island of Arran has been taken in hand by 



