408 Notices respecting New Books. 



may have a direct bearing on questions of the highest importance 

 from a most utilitarian point of view." 



The frontispiece is a woodcut-diagram showing the probable po- 

 sition of these lowest and far more ancient rocks, crumpled up and 

 worn down, on which the Lower Cretaceous sands and clays lie 

 unconformably. 



Many points of interest to the geologist, whether tyro or ad- 

 vanced, occur throughout this memoir. The mistaken notion that 

 half-taught students get of the so-called London " Basin " is held 

 up to caution (p. 3), and the relation of this synclinal trough to the 

 saddle-back of the Weald, and the hollow fold of the Hampshire 

 area is noticed (p. 69) j as well as the subordinate flexures and faults 

 at "Windsor, Deptford, and Purfleet (pp. 21 and 70), like that at 

 Portsdown (we may add), though smaller, and others, which may 

 affect the well-being of the proposed Channel Tunnel. The sub- 

 terranean erosion of the Chalk by acidulated waters is noticed at 

 pp. 25, 2(3. The nature of flint is referred to at p. 19 ; but nothing 

 satisfactory or new is advanced ; and the very probable theory of 

 pseudomorphism of silica after limestone is not noticed, though 

 applicable even to the so-called vein-flint, where on both sides of 

 a fissure the chalk itself, with some of its fossils, is changed into 

 flint, as in the nodules themselves. 



This admirably concise and useful memoir ends with a well- 

 written page or two on " Denudation, its nature and effects." But 

 we must be allowed to doubt whether the denudation, or surface- 

 sculpture, of the London district has been wholly worked out by 

 rain and rivers. It was not so very long ago, geologically speak- 

 ing, that a wide| expanse of shallow waters (whether marine, estu- 

 arine, or freshwater, is not yet clear) left banks and shoals and 

 wide areas of gravel, sand, and loam spread out over all the district 

 from Chalk-range to Chalk -range (referred to at p. 57). These 

 shallow waters must have retreated, slowly or rapidly, uniformly or 

 by fits and starts ; and both river-currents and retreating tides leave 

 valley-furrows on deserted shoals and banks of mud and shingle. 

 Hence it would be strange indeed if the gravels, clays, and sands 

 of this district, so near the present level of the eea and connected 

 with British ground that has subsided even 1000 feet below the 

 Glacial Sea and risen again, should not have been worn by the re- 

 treating sea into valleys of drainage which have since been widened 

 out and eaten further back by snow and ice and rain and rivers. 



Por all who wish to understand the geology of London and 

 its neighbourhood, the map, the model, and the memoir are in- 

 dispensable ; and an intelligent interest, indeed a philosophic life, 

 is imparted to the dry details of descriptive geology by the com- 

 prehensive and well directed knowledge of the talented author of 

 the memoir. 



