Revieivs — WMtalxers Geological Model of London. 515 



areas in preference to others is made ver^r apparent. Mr. Prestwich, iu 

 his admiraljle Presidential Address to the Geological Society last year, 

 entered into some interesting details to show how unerringly, np to 

 the time of the great Water Companies, the population had followed 

 the great gravel-bed on either side of the Thames. "A map of 

 London so recent as 1817 shows how well defined was the extension 

 of houses arising from this cause. Here and there onl}'- beyond the 

 main body of the gravel there were a few autliers, such as those at 

 Islington and Highbury ; and there habitations followed. In the same 

 way south of the Thames villages and buildings were gradually ex- 

 tended over the valley-gravels to Peckham, Camberwell, Brixton, 

 and Clapham-; wiiile, beyond, houses and villages rose on the gravel- 

 capped hills of Strcatham, Denmark Hill, and Norwood. It was 

 not until facilities were given for an. independent water supply by 

 the rapid extension of the works of the great Water Companies that it 

 became practicable to establish a town population on the clay districts 

 of Hollowa}'-,. Camden Town, Regent's Park, St. John's Wood, West- 

 bourne, and Netting Hill." The valley of the Lea shows the same 

 geological causes at work localizing the population in accordance 

 with the primary need of life. A little outside the northern limits 

 of the Model we should find the presence of the gravel-beds indicated 

 by the more or less historical settlements of Hendon, Stanmore, 

 Finchley, Barnet, Totteridge, Whetstone, and Southgate. 



The spread of the river-gravels and loams up the gentle slopes of 

 the Thames Valley several miles on either side, and to a height of at 

 least 80 feet, tells its own story as to the former width of the pre- 

 historic river which was the precursor of the present diminished 

 stream. The vivid manner in vsdiich the old and not yet obsolete 

 physical geography of the country is pictured is one of the great 

 merits of the Model. Perhaps the great superiority of a model over 

 a plane surface consists in the fact that it puts before us the actual 

 dynamical conditions to which the landscape is subject, and under 

 which the contours of one age are gradually passing into those of 

 another. 



The gravels of this part of England form at present an unwritten 

 chapter of Post-glacial geology. Speaking broadly, it may be 

 said that the first term in the series is that accumulation of the 

 Glacial Period which underlies the chalky clay. This dej)osit (the 

 " Middle Glacial of the South-east of England," as Mr. S. V. Wood, 

 jun., has named it) is the great fund from which the subsequent 

 accumulations in all their varieties have been drawn. But between 

 this genuine glacial gravel (mostly Hint, but with foreign rocks and 

 an abundance of the Oxford Clay Gryphea) and the valley-gravels, 

 with their remains of Mammoth and Ehinoceros, the process of 

 assortment and removal to lower levels has given rise to local 

 modifications of a marked kind. These local characters which the 

 gravels put on in and around London doubtless represent a long 

 period of great changes in the hydrograpliical and terrestrial con- 

 ditions of the country, and open jiaths of investigation which will 

 be well worth following up. We look forward to the forthcoming 



