A HISTORY OF HERTFORDSHIRE 



It is evident that boulder-clay once filled up most of our valleys 

 as well as covered all but our highest hills. In the east of the county 

 the sources of our rivers are upon it ; the rivers then cut through it in 

 places into the Chalk ; and lower down their valleys the boulder-clay 

 has been completely cut through by them, exposing the underlying 

 Glacial gravel and sand. 



After the deposition of the boulder-clay the land again rose, but not 

 for some time to its present level, the old shore-lines which pass through 

 the southern counties, where they have left their mark in beach-shingle 

 and sea-cliffs, being evidences of successive elevations of the land, at one 

 time up to 140 feet below its present level, and subsequently to within a 

 few feet of it. 1 The shingle-beaches at various levels indicate pauses in 

 the upheaval, and by the time the sea had receded (or rather the land had 

 risen) so far as to form a shingle-beach at least 100 feet higher than 

 that now forming on our coasts, the arctic climate had given place to 

 one milder than that which now prevails. 



This period of upheaval marks the time when marine gravels finally 

 ceased to be formed above the present sea-level, giving place to estuarine, 

 alluvial, and lacustrine deposits. An instructive example of the latter is 

 the ancient Hitchin lake-bed, for the most complete knowledge of which 

 we are indebted to Mr. Clement Reid, 8 although it has also been 

 investigated by Sir John Evans, Mr. William Hill, Mr. William Ransom, 

 and other Hertfordshire geologists and archsologists ; for the formation 

 of this lake-bed and the overlying deposits embraces the period during 

 which the study of geology gives place to that of archasology, bringing 

 Man upon the scene. 



The alluvial or lacustrine deposits known as the Hitchin lake-bed 

 lie in a channel or trough running nearly north and south, which appears 

 to have been excavated, or re-excavated, after the deposition of the 

 boulder-clay, the geological position of the lake-bed being between the 

 great chalky boulder-clay, representing the close of the Glacial period in 

 this neighbourhood, and the brick-earth in which Palasolithic flint 

 implements are of frequent occurrence. The deposit is very variable in 

 character, consisting of sandy, marly, and loamy beds, white, yellow, 

 brown, and black, sometimes, from the abundance of decomposed plant- 

 remains, even forming a lignite. It contains the teeth and bones of 

 several mammals and fishes, remains of a few insects, the shells of many 

 molluscs, the leaves and seeds of numerous flowering plants, several mosses, 

 and a few charas. Most of the species still exist with us, but all the 

 mammals have long been extinct in Britain in a wild state, and two, 

 the mammoth and woolly rhinoceros, are altogether extinct. Their 

 remains have all been found in a whitish marly silt which occurs locally 

 above the deposits from which all the other fossils have been obtained. 

 On this silt rests the Paleolithic brick-earth, which until recently yielded 



1 Clement Reid, Victoria History of Hampshire, vol. i. p. 23. 



' The Paleolithic Deposits at Hitchin and their relation to the Glacial Epoch,' Prac. 

 Royal Soc., vol. Ixi. p. 40 (1897) ; Trans. Herts Nat. Hist. Sac., vol. x. p. 14 (1898). 



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