432 PKOCEEDIK-GS OP THE GEOLOGICAL SOCIETY. [Mar. 21, 



in the fact tliat fossils from a bed of sand below the London Clay 

 have been mistaken for Crag species (see pp. 416-418) ; for if old 

 Tertiary shells in fairly good preservation show such a likeness to 

 those of the Crag as to be mistaken for them, how much more 

 likely are we to be led astray by mere casts and impressions, such as 

 those from Lenham ? 



Since this paper was read, there have appeared two abstracts of a 

 note by MM. Cornet and Briart " On the Discovery in Hainaut, below 

 the Thanet Sands, of a Limestone with a Tertiary FauLua"*, most of 

 the species being allied to those of our Barton and Bracklesham Beds ; 

 in other words, there is a Middle Eocene fauna at the bottom of the 

 Lower Eocenes. Surely this should lead us to' be careful in deter- 

 mining the exact position of Tertiary beds by their fossils alone. 



Those who agree as to the comparatively modern age of the sands 

 on the North Downs are at issue as to their exact position. Mr, 

 Prestwich refers them to the Lower or Coralline Crag. Sir C. Lyell f 

 has thrown them down into the Miocene ; and, last of all, a foreign 

 palaeontologist has lifted them up higher than before, as may be 

 seen from the following translation, for which I have to thank Mr. 

 Jenkins, the Assistant-Secretary : — " Moreover the iron-sandstones 

 of Kent, which Lyell misquotes as Miocene, contain no single typi- 

 cal Miocene species, but many which are referable to species charac- 

 teristic of the Upper Crag — a fact of which I have convinced myself 

 by an inspection of the collections of Mr. Prestwich and of the Geo- 

 logical Survey ; these beds must therefore be considered Pliocene %. 



It seems to me that Dr. von Koenen is somewhat rash in saying 

 that these beds must be considered Pliocene ; he has seen the fossils 

 only, and not the beds they came from ; but he has told me that his 

 opinion was backed by the late Dr. S. P. Woodward, an authority 

 second to none in the determination of recent and Pliocene shells. 

 Mr. S. y. "Wood and Mr. Charlesworth, however, say that the fossils 

 cannot be determined with accuracy, as they are only casts. 



"With regard to the placing of these sands in the Miocene System 

 by Sir C. Lyell, I cannot help remarking how that age seems to be 

 used in England as a sort of harbour of refuge for Tertiary rocks. 

 Wherever there are Tertiary beds of which the age is doubtful (that 

 is to say, which are not capped by any other deposits, or are capped 

 by drift only), those beds have been, at one time or other, called 

 Miocene — for instance, the Bovey Beds of Devonshire, the Hempstead 

 Beds of the Isle of Wight, and the Leaf-beds of MuU. Moreover, 

 when Tertiary formations are classified by their contained plant- 

 remains, the worst of all fossils for such a purpose, the odds are 

 greatly in favour of their being called Miocene. Bovey, Hempstead, 



* Geol. Mag. vol. iii. p. 174, and Quart. Journ. Geol. Soc. vol. xxii. part 2. 

 p. 11. 



t Elements of Geology, 6th edit., pp. 233, 368 (1865). I believe that Sir 

 Charles Lyell has since given up this opinion, and now looks on these sands as 

 Crag. 



\ " Die Fanna der unter-oligocanen Tertiarschichten yon Helmstadt bei 

 Braunschweig," by Dr. A. von Koenen, Zeitschr. der deutsch. geol. Gesellschaft. 

 vol. xvii. p. 461 (1865). 



