INTRODUCTION. 3 



As will be seen, they furnish records of two distinct chapters 

 in geological history. The London Clay was accumulated in an 

 estuary and sea to which was carried the mud of an ancient river 

 long before the present physical features were developed, and 

 when the climate, as indicated by fossil remains of animals and 

 plants, was sub-tropical in character. The Valley Gravel belongs 

 to early stages in the history of the Thames, when climatic 

 conditions were at times like those of the present day, but with 

 evidence of more torrential action than we now witness. The 

 fossils of the gravel and its associated brickearth are of great 

 interest, and include remains of mammoth, rhinoceros, hippo- 

 potamus and other animals long extinct in the area; and with 

 them are found ancient stone implements manufactured by 

 man. These Valley formations underlie the greater part of 

 London between Islington and Camberwell and between Brentford 

 and the Lea 1 Valley. 



We have not, however, to go far north before we meet with 

 other formations, the fine sands .on Hampstead Heath, known 

 as the Bagshot Beds, and the chalky clay full of stones and 

 boulders at Finchley, known as the Boulder Clay, a product of 

 the Ice Age; while on the south-east between Lewisham and 

 Woolwich and Erith there are great excavations in the Chalk, 

 a comparatively deep-sea formation, covered by shallow-water 

 marine and estuarine Eocene strata. 



The several geological formations thus have each a story 

 that can be deciphered, of great changes in physical conditions 

 and in life history. Although the record of events is far from 

 complete in our present area, yet we are enabled to picture the 

 successive scenes of deposition and denudation, and the forms 

 of life, which lead up to those of the Pleistocene period with its 

 relics of palaeolithic man ; while onwards we come to the Recent 

 or Holocene period, which, beginning in Neolithic times, has 

 a fairly connected record through the Bronze and Iron ages to 

 historic times and the present day. 



The story of London is usually reckoned to commence less 

 than nineteen hundred years ago, when the Britons, who had 

 established a kind of fortified settlement on the rising ground 

 now dominated by St. Paul's Cathedral, were displaced by the 

 Romans (about A.D. 43). The reasons for the selection of the site 

 and the influence of the geology on the subsequent growth of 

 the Metropolis are discussed in the last chapter. 



For a study of the geology open sections of the strata are 

 necessary; in and around London these are always numerous 

 on account of the ever increasing works of the builder, though 

 most of the pits and excavations are of a temporary nature. 

 One object of the present work is to give such descriptions as 

 may enable the student to identify the different formations in 

 fresh exposures, and to further our knowledge by recording 



1 The] spelling ' Lee ' is more correct, but ' Lea ' has been adopted on 

 the maps. 



