2ET. 45.] CORRELATION OF TERTIARY STRATA. 103 



I am, however, not yet quite satisfied on the question of parallel- 

 ism, nor is it one on which I would venture on a positive opinion 

 without the few months' research I hope to be able to devote to 

 it this summer. At present, however, I am inclined strongly to 

 place the Gres de Fontainebleau in the Eocene period. 



I think it will be a great pity to break up these great time 

 divisions into small sections. Let us have, if they like, Lower, 

 Middle, and Upper Eocene, and Miocene, &c., but not a multitude 

 of terms founded on that base. . . . Yours very truly, 



J. PRESTWICH. 



J. Prestwich to Sir Charles Lyell. 



[14] CLIFTON ROAD EAST [ST JOHN'S WOOD], 12th Jany. 1857. 



MY DEAR SIR CHARLES, The pressure of business, of family 

 engagements, and a visit to consult various books on the subject 

 of your inquiry, have been the cause of too long a delay in 

 answering your last notes. 



The correlation by Forbes of the Hempstead series with those 

 of Limburg seems correct enough, but the English beds are so 

 much related to those beneath the Belgian beds also, tho' possibly 

 to a lesser extent; whilst, according to Hebert and others, the 

 Gres de Fontainebleau is so little, or is rather so very distinct, 

 that I cannot yet feel quite satisfied that there is not an error 

 somewhere or other. 



I cannot reconcile myself to the association in the same time- 

 division of the Faluns of Touraine and the Fontainebleau Sands. 

 It is true that if the former are to be excluded, the Miocene 

 period becomes reduced to very narrow limits, or rather ex- 

 hibition, in France and England ; but then there is the point to 

 which you allude, whether in other parts of Europe we may not 

 find the time marks, the strata of that period. I think we must. 



If the Miocene has yet to have its limits defined, and the 

 Fontainebleau Sands are to be considered as the commencement 

 of a new period of change, then I think we must look elsewhere 

 than in the French Faluns for the maximum development of its 

 peculiar types. I should not at all object in that way to take 

 the Fontainebleau Sands as Lower Miocene, filling up the centre 

 and top with German or yet to be discovered beds, but then I 

 should feel inclined to take the Faluns of Touraine as part of 



