Reviews — NottinghavisJtire Water Supply. 475 



distribution. Tlie same applies with perhaps even more cogency 

 to the recent attempts to introduce a third, spilitic, series, which 

 appears to differ in no fundamental character from either of the other 

 two. The spilites appear to be simply normal basalts in which the 

 soda molecule has been concentrated by some kind of pneumatolysis 

 or differentiation, which in this respect are really much the same 

 phenomenon under different names. 



Perhaps the least satisfactory part of the whole treatment is the 

 explanation that is offered for the highly alkaline rock-types, 

 nepheline syenites, phouolites, leucite rocks, and so forth. For this 

 is given what appears at first sight the paradoxical explanation that 

 they are due to the assimilation by sub-alkaline magmas of limestone 

 or dolomite. These materials are supposed to act as powerful fluxes, 

 greatly facilitating the differentiation of the magma, and leading to 

 concentration of its salic constituents in one portion and its calcic and 

 feraic molecules in the other portion. Evidence is brought forward to 

 show the extremely common association of such exaggeratedly alkaline 

 rock-types with limestones in rocks of all ages. Here and elsewhere 

 great importance is attached to the idea of the so-called ' two-phase 

 convection' as an agent of differentiation. Space will not here 

 permit of a discussion of the validity of this conception, which is 

 obviously of very great importance. 



It only remains to express the thanks of the petrological world to 

 Professor Daly for bringing forward such a notable contribution to 

 scientific petrology, which is bound to have a far-reaching effect, and 

 by its frank and fearless discussion of many accepted dogmas must 

 eventually help us in our slow progress towards the truth. 



H. H. R. 



II. — The Watkr Supply of Nottinghamshire from Underground 

 Sources. (Memoirs of the Geological Survey, England and 

 Wales.) By G. W. Lamplugh, F.R.S., and B. Smith, M.A. ; 

 with a chapter on the rainfall by H. B. Mill, D.Sc, LL.D. 

 pp. 174, with 2 plates and 2 text-figures. Price 5s. 



THIS memoir forms a notable addition to the series on the Water 

 Supply of English Counties. The underground water is of 

 great economic importance, since almost the whole of the supply 

 is now derived directly from this source, the surface-water being in 

 nearly every instance too much contaminated for use. The rocks of 

 the county are fortunately peculiarly well adapted for the absorption 

 and storage of the rainfall, and the most extensive of the water-bearing 

 formations is conveniently situated for the supply of the industrial 

 centres. 



In ch. i an outline is given of the arrangement and character of the 

 geological formations. The general dip of the strata is to the east in 

 the northern part of the county, swinging round to the south-east in 

 the southein part, and it is almost everywhere at a low angle, rarely 

 so much as 5 degrees. A geological map on the scale of 4 miles 

 to 1 inch forms plate i, and on this lines are drawn to indicate the 

 contours of the top of the Bunter beneath the overlying formations, 



