104 CORRELATION OF TERTIARY STRATA. [l857. 



another time stage. I was not at all satisfied from what I saw 

 at Bordeaux of the connection there said by some to exist be- 

 tween the equiv. of the F. Sands and the Faluns. The Fal. 

 of Leognan are said to underlie certain freshwater limestones 

 said to be synchr. with those of La Brise" this was not at all 

 clear to me. One fact was very [clear], that the Fal. of Sancats 

 did overlie that limestone, and that the latter probably overlaid 

 the Font. Sands ; but then between the limestone and the Sancats 

 Fal. I found no passage on the contrary, I found a marked 

 division. The limestone was all fresh-water, and its surface was 

 worn and covered with the holes of boring molluscs. I think this 

 had not been noticed before. . . . With regard to the other 

 questions you ask me, I think the Barton Beds at Barton form 

 quite an exceptional state of things. I have shown in my last 

 paper that that series is exceptionally a sandy series, and that 

 the clays set in in places, and I take the Headon Hill Sands 

 as rather the type than the exception. Certainly the line should 

 not, I think, be drawn between the Barton Clays and the Headon 

 Hill Sands. I think I shall draw my next sub-line at the base 

 of the old Upper Marine, but to this point I have not yet come. 



I am most anxious to see Forbes's work on the Isle of Wight, 

 to study more accurately the fossil evidence he has based his 

 divisions upon. I hope shortly to have more leisure to resume 

 geology and to attend to treasurership duties. In the meantime I 

 am snatching a few moments to get a paper ready for the next 

 meeting. The subject will, I think, interest you, " Crag on the 

 North Downs." Yours very sincerely, J. PEESTWICH. 



J. Prestwich to the Same. SUFFOLK LANE, Monday, 9th Feb. 1857. 



MY DEAR SIR CHARLES, I do object very much to placing the 

 Sables de Bracheux on the parallel of the Thanet Sands. It is 

 possible, however, that the latter may come into some part of 

 the French area ; and in mineral character there would be so 

 little to distinguish them that they would all pass under the 

 name of the G-lauconie Infe'rieure, but I think they would be found 

 to pass under the S. de B. 



I know of no solid argument adduced by Hebert. It is a 

 point I worked out with great care, and it was only after a 

 long time that I obtained evidence to be depended upon. It 



