J. S. GARDNER ON" THE LOWER LONDON" TERTIARIES. 209 



represent some such action (but under a rougher sea) as that which 

 now forms the beach at Shellness, not far off; and it is conceivable 

 that if this were an area of gradual depression, as it was at the 

 commencement of the London-Clay period, the beaches there would 

 advance steadily over the flat area of Sheppey on the one hand, while 

 on the other, as they sank out of reach of disturbing waters, they 

 would become covered up by the silt of the Thames, just as the Oldha- 

 ven beaches were covered by the London-Clay silt of the Eocene river. 



The depression was maintained for an enormous period, the salt- 

 water estuary gradually extending up the river- valley as far as the 

 western limits of the Hampshire basin, and deepening at Sheppey 

 until nearly 500 feet of silt was deposited. The Thames mud at 

 the same spot is already nearly 100 feet thick, and this on the present 

 shore and consequently out of the main channel. The advance of 

 the London-Clay sea was distinctly not due to any planing action, 

 but to gradual subsidence ; for the London Clay always rests on 

 other Eocene formations, though elsewhere and far off the Chalk 

 must have been incessantly attacked, as it is now, by the waves. 

 Beaches such as the Oldhaven deposits could only be formed near 

 the mouth of the river ; and we accordingly see that they diminish 

 and disappear in Hampshire and to the west. 



Beaches may equally have been formed along the shore of the Thanet- 

 Sand sea, and left stranded when it retired ; and it is not always clear 

 to which agency many of the vast aggregations of shingle and sand 

 between the Thanet Beds and the London Clay may belong. They 

 are, however, an integral portion of one or other formation, and 

 should not be recognized as a separate formation at all approaching 

 other divisions of the Eocene in value. The same may be said of 

 the so-called marine Lower Bagshots, which mark the retreat of 

 the London-Clay sea. That any vast lapse of time occurred between 

 the Thanet-Sand and London-Clay period I do not at present believe, 

 seeing that the enormous change of temperature that almost suddenly 

 took place between them, a change which drove the indigenous flora 

 northward to Greenland, would amply account for the difference 

 in their faunas. The Woolwich Beds at least, however, were 

 formed during the interval, and the European Tertiaries may furnish 

 data as to its duration. 



I submit this as a simpler explanation of the formation of the 

 Lower London Tertiaries, and a more definite classification of their 

 complicated changes, than that hitherto prevailing. If accepted, it 

 can by no means diminish the value of any work previously accom- 

 plished ; and, while involving no new terms, it renders the recogni- 

 tion of the divisions in the field far easier. 



Discussion. 



Prof. Prestwich remarked upon the value and beauty of the 

 collections made by Mr. Gardner. At the time he had written his 

 own paper the exact horizon of many forms had not been deter- 

 mined, and the careful collecting of Mr. Gardner would clear up 

 many of thes6 doubtful points. He did not, however, think that 

 the theoretical views propounded in the paper were of equal novelty 



