WATFORD NATURAL HISTORY SOCIETY. xlvii 



of which were waved. The chalk was evidently cut out in a 

 hollow before the clay Avas deposited, showing a very great interval 

 of time between the deposition of the chalk and of the clay above. 

 Elsewhere such hollows were nearly always caused by the sinking 

 of the overlying beds through the dissolving away of the chalk. 

 The .clay could not be older than the boulder-drift, and he would 

 call it glacial drift, though Dr. John Evans and other geologists 

 believed it to be post-glacial. The mistake was often made of 

 supposing all beds termed "glacial" to be considered by geolo- 

 gists as having been deposited by ice or in an arctic climate, 

 but all that was meant by the term was that such beds were 

 deposited during the glacial epoch, in which were intervals of 

 warmer climate as well as cold periods. The bed now seen 

 looked like some beds of brick-earth which elsewhere occurred 

 under boulder-clay, and it might have been formed in some lake of 

 no very great extent. On the top of this clay might be seen a bed 

 of gravel, but he could not say whether it was a river-gravel or a 

 glacial gravel. If it belonged to the glacial period, the beds of clay 

 below must also be glacial. Glacial and post-glacial were, how- 

 ever, only relative terms, for glacial conditions lasted longer in the 

 north of England than here. 



On leaving the chalk-pit the road past Bushey Station was taken, 

 and from an elevated position above Wiggenhall, affording a good 

 view of the valley of the Colne and the hills on either side, Mr. 

 Whitaker pointed out the connexion of the superficial features of 

 the country with its geological structure. The range of hills on 

 the edge of which we now stood was, he said, known as the Tertiary 

 escarpment, the term "escarpment" meaning a ridge along which 

 the beds were " cut off." These Tertiary beds once extended much 

 farther over the county, and the escarpment was at one time be- 

 yond its present position, as shown by outliers of the London Clay 

 and Reading Beds. The Colne had most probably determined the 

 present line of the escarpment by cutting its way back, but further 

 down it had cut through the beds. If we had been higher, we 

 should have seen that the slope on the opposite side of the valley 

 rose gently to a greater elevation than this, and we should find 

 that this higher ground consisted of gravel flats of the same 

 character as the one we had just walked over, the river having 

 cut away the beds between. 



The valley of the Colne was then crossed, and at the Colney 

 Butts gravel-pits Mr. Whitaker stated that the gravels seen be- 

 longed to the glacial drift and were probably of marine formation, 

 for in some places, as in Suffolk, marine fossils were found in 

 sandy beds of similar age. The larger stones, perfectly rounded, 

 must, he said, have come from the north ; the pink quartzites were 

 supposed to have come from the Lickey Hills ; and the flint-pebbles 

 had come from Tertiary beds, in which they had originally been 

 deposited after the denudation of the chalk in which the flints were 

 first formed — a vast quantity of chalk having been denuded to form 

 such extensive gravel beds. 



