1866.] WHITAKEE LOWER LONDON TERTIAEIES. 405 



papers*; and secondly, because a detailed account of all of them 

 will appear in future Geological Survey Memoirs. 



It is also needless to notice earlier authors, as Mr. Prestwich has 

 giv.en a full list of them. 



Although the Geological Survey of the district in question is not 

 yet finished, still so little is left undone that there can be no doubt 

 as to the general correctness of the observations on which this paper 

 is founded. 



It should be stated that, although the whole of the district is 

 known to me, I have not myself surveyed all of it, Mr. Hughes being 

 answerable for the mapping of the country between Eochester and 

 Faversham, and Mr. Dawkins for some part of the neighbourhood of 

 Faversham. All the rest is my own work, the unfinished parts 

 being on the east of Eltham, in the neighbourhood of Erith, and 

 around CHfie and Halstow, between the Thames and the Medway. 



The more I have learnt of the Tertiary beds, the more have I seen 

 reason to agree with Mr. Prestwich's views ; and, indeed, all he has 

 left to do is the filling-in of his outlines, the addition of a few de- 

 tails which seem to have escaped his notice, and a change in nomen- 

 clature in a matter that he looked on as doubtful ; in fact I only 

 differ from Mr. Prestwich in questions on which he has spoken 

 with doubt. 



The beds between the London Clay and the Chalk, of which this 

 paper treats, are of far greater interest in Kent than elsewhere, and 

 for these reasons : — 1, that they are there most fully developed ; 2, 

 that their structure is there more complex and shows more change 

 than anywhere else ; 3, that there are many fine sections ; and, 4, 

 that they are almost without fossils in all other districts. These 

 beds might indeed be well called " the Kentish Tertiaries." 



§ 2. Thanet Beds. 



The indefinite word " Beds " seems to me better than the more 

 definite " Sands " or " Clays," as it is somewhat uncommon for a 

 formation to have everywhere the same lithological composition; 

 and I have therefore used the above name rather than that of 

 "Thanet Sands." 



(«)t At the base of this set of beds, and resting at once on the 

 Chalk, there is always a clayey greensand, with unworn green-coated 

 flints at the bottom ; to this the name of the " Base-bed " may be 

 given. Mr. Prestwich has called the like part of the London Clay 

 the " basement-bed" +; and I have named that of the Woolwich 

 and Eeading Series the " bottom-bed "§. By using a different 

 name for each of these marked layers, one is saved the repetition of 

 the names of the formations to which they belong. 



This is the only part of the series which is constantly present, 



* Quart. Journ. Geol. Soc. vol. vi. p. 252 ; vol. viii. p. 235 ; and vol. x. p. 75. 

 t The letters a, b, a, j3, &e.,and the numerals 1, 2, &c., refer to those by which 

 the several beds are distinguished in the sections in PI. XXII. 

 t Quart. Journ. Geol. Soc. vol. vi. p. 255 (1850), 

 § Oeol. Survey Mem. on Sheet 13, p. 23 (1861). 



