364 Bibliographical Notices. 



of these lectures ; and we think that the Council of that Institution 

 have acted wisely and conferred a benefit in requesting the author to 

 embody them in a more permanent form. In this manner we are 

 enabled to consult at our leisure the details of those well-explained 

 conclusions, to which we, as well as others doubtless, listened with 

 so much pleasure. 



Although apparently confined to the ' Geology of Clapham,' this 

 work really takes a wider range, and describes the nature and cha- 

 racter of those geological changes which have taken place in the 

 vicinity of London, embodying at the same time the principal results 

 arrived at by geologists, and a statement of the mode by which the 

 several problems have been worked out. These lectures are divested 

 as far as possible of all technicalities ; explanatory notes and refer- 

 ences, as well as small but useful illustrations, are given, so as to 

 render the description of the records of the successive physical phse- 

 nomeua which are preserved in the ground beneath us, intelligible 

 to the ordinary reader. 



The first lecture is devoted to one of the later, if not the latest 

 period of the earth's history, — the accumulation of the superficial 

 gravel and its associated beds : no geological subject is of more diffi- 

 cult iuquiiy, few perhaps so interesting. Most of our readers who 

 have examined the excavations for sewage, building, or for the mate- 

 rial itself*, are aware that in and around London there is a vast 

 accumulation of gravel, which gravel varies from 3 to 20 feet or 

 more in thickness. The origin of this gravel, the direction from 

 which it has come, the agency by which it has been brought, the 

 period at which it was distributed, and the fact of its being the great 

 source of water-supply to all the shallow wells and land-springs in 

 the district, — are points fully and succinctly treated. 



The main bulk of the gravel of Loudon has been derived from the 

 black flints which occurred in the surrounding chalk districts ; but 

 this destruction of the chalk must have been very considerable, for it 

 is inferred by the author that it would require a mass of chalk 200 

 or 300 feet thick to form a bed of flint-gravel 10 feet thick. With 

 the flint-gravel occur cretaceous sandstones, and also, but more 

 rarely, pebbles of quartz, porphyry, and slate, which must have been 

 transported from some distance, as from Wales and the border coun- 

 ties. Mr. Prestwich treats of the possible modes of transport, in- 

 ferring, with other geologists, that the surface now covered by gravel 

 was under water at the time, and that the distribution might have 

 been effected either by the transient action of a body of water, — or 

 by the action of a large river flowing into the Thames valley, — or by 

 the ordinary power of sea-currents, — or by the agency of coast-ice 

 and icebergs. One fact appears evident, that the surface of the 



* The value of this gravel, and its general use for road- or pathways, is 

 well known, and even also as a material for exportation. Some years 

 since, a large quantity was exported from Bayswater to Russia, realizing a 

 considerable sum ; and hence, we believe, the origin of local names of 

 buildings and places in tliat neighbourhood. 



