48 Mr. Henry Walker's Lecture : 



very few years of continuously equable climate would liave 

 sufficed for the change of habitat. How near Essex and 

 Middlesex were to the southern migrants is shown by the 

 presence of the fluviatile Cyrena in the tepid waters of the 

 Thames." 



Such, then, were the geographical conditions and climatal 

 fluctuations in Pleistocene Britain. Familiar as we are 

 with the far different conditions of our country to-day — 

 with the isolation of Britain from the Continent, and the 

 ascendancy of man over the animal world — it is difficult 

 to realise the Britain of this earlier period. Yet this 

 union of England with the Continent, this overlapping in 

 Essex and Middlesex of the range of the Arctic and sub- 

 tropical fauna, exceptional and abnormal as it at first sight 

 appears, may have lasted for a very considerable length of 

 time. It will hardly be doubted by geologists that this 

 continental stage of our country's history far exceeded in 



* " When the temperature of the river water was congenial to the 

 Cyrena above mentioned it was also suited to the liippopotamus." — 

 Sir Charles Lyell : " Principles of Geology," 10th edit., vol. 1, page 

 192. In the year 1863 the author of the " Principles " propounded 

 that interpretation of the zoological phenomena in question wliich is 

 now generally accepted. It is summed up in the last edition of the 

 " Elements of Geology," for 1871, p. 138 : " . . . The apparently conflict- 

 ing nature of the e\T.dence may be due to the place of our observations 

 bemg near the boundary line of a northern and southern fauna, either 

 of which may have advanced or receded during comparatively slight 

 or temporary fluctuations of climate." A valuable collection of 

 zoological data in suppoii; of tliis ^iew has been collected by Mr. Boyd 

 Dawkins, and is now published in his " Early Man in Britain," 

 1880. The stratigraphical evidence is a far different matter, invohing 

 more difficult and onerous labours, and when this shall have been 

 completed, and the exact succession of ; geographical events and cli- 

 matal phases of the period in question be detailed to us, some very 

 important lacuna in the history of the northern and southern fauna 

 of the old Thames Valley will have been filled up. — [In order to show 

 in a general way the relation of the various beds forming the country 

 around Epping, I have given (see frontispiece) five lines of sections 

 which I have taken from a series kindly lent to me by INIr. Searles V. 

 Wood, Jun. The beds numbered 6 and 8 differ somewhat, inter se, 

 (in a way which is beyond the scope of this lecture to describe), but 

 they bear that relation to 7 which their numbers import.] 



