104 Correspondence — Mr. A. H. Green. 



Tertiaer-conchylien), of Semper (Palseontologische Untersucliungen), 

 and of Speyer (who has described and figured a large number of 

 fossils exactly, from these beds in Palaeontographica), — that is to say, 

 according to all the important works published on that subject in 

 the last ten or fifteen years. The opinion of Mr. Nyst, who of 

 course is the best judge about Belgian Tertiaries, has been cited 

 against me, but this was his former opinion ; it is now quite in 

 conformity with mine after the discoveries of the last few years. 

 Lastly, I must repeat that it is possible, and therefore necessary, to 

 divide the Tertiary deposits into far more than two, four, or six 

 periods. It is of no consequence which names are adopted for them, 

 whether the names Eocene, Oligocene, Miocene, and Pliocene are 

 associated with Lower, Middle, and Upper, or whether we use the 

 names given by Prof. Ch. Mayer at Ziirich to all the different 

 ** Etages." A. von Koenen. 



Makburg, Prussia, 20^7i Dec.^ 1867. 



THE OUSE VALLEY. 

 Sir, — I am sorry that the mistake into which Mr. Searles Wood 

 has fallen respecting the quarter-sheet 45 N.E., of the map of the 

 Geological Survey of England and the Memoir thereon obliges me 

 to request space for self-defence. Mr. Wood's charge is that I have 

 omitted " all reference to the Glacial Clay." It is true that I have 

 not sub-divided the Drift of that country into an upper clay and a 

 lower gravel, because, as far as I could judge, I did not find evidence 

 to support such a classification ; but I have very distinctly stated 

 that Boulder-clay is one of the forms which the Glacial deposits take 

 (p. 53 of the Memoir), and have described sections where the clay 

 is to be seen (p. 57). The Glacial Beds are not laid down on the pub- 

 lished map because, as I have mentioned in the Memoir (p. 59), 

 " additional surface maps are in course of preparation, on which the 

 areas covered by superficial deposits will be marked out ;" adding, 

 what every one who has tried the experiment knows very well, 

 that " it would be impossible, on the one-inch scale, to show these 

 beds and the stratified rocks on the same map." 



With respect to the sections on p. 34 of the Memoir, and p. 564 of 

 your last volume, which Mr. Wood finds so different, I have only to 

 state that the first has one scale for heights and another for distances, 

 so that the former are exaggerated ; the other is drawn to something 

 like a true scale. In the one case too the outline of the supposed 

 ancient valley is rashly drawn hard, and in the other indicated by a 

 dotted line. The facts represented are exactly the same in each case, 

 and I take it rather hard that I should be blamed because four years ; 

 experience has made me cautious and, may-be, rather a betterd raughts- 

 man. I have no wish to set up my own limited experience, which 

 I have urged in the Memoir (p. 58) as a reason for refraining from 

 theorising, against the widespread and long-continued researches of 

 Mr. Wood ; but I do expect him, before he criticises, to do me the 

 justice to read my memoir more carefully. A. H. Green. 



Monk Bretton, Barnsley, January lUh, 1868. 



