Corresjioyidence. 665 



Hill House, contain nearly all the testacea now living in our rivers, 

 and none of those extinct in Britain, and no bones of mammals, 

 proves them to be much newer than the neighbouring deposits con- 

 taining older forms of life. 



Again, the principal object of the essay seems to be to demonstrate 

 the Post-glacial age of the valleys in the south-east of England, 

 and especially that of the Thames. That demonstration has al- 

 together eluded my grasp. An appeal to the author's elaborate 

 maps, in the rooms of the Geological Society, supplies proof that 

 is directly subversive of his theory. The whole question lies in 

 a nutshell. Do you, or do you not, find Boulder-clay in the basins 

 drained by the rivers (jf which he writes ? Is it present in those of 

 the Eoding and Blackwater ? A glance at Mr. Wood's map of the 

 area drained by the former, shows that he recognizes that it is so 

 found. In reference to the latter river I have to correct a mistake. 

 Mr. Wood wrote to me for proof of its occurrence in the basin of 

 Blackwater ; and, unfortunately, without dreaming that my hurried 

 note would be quoted in print, instead of referring to my note book, 

 I ran my finger up an affluent of the Blackwater, instead of the 

 main stream, and wrote Ingatestone and Mountnessing, — a mistake 

 that Mr. Wood has italicised and noted with a mark of admiration. 

 I ought to have written Witham Station. So far, indeed, as Mr. 

 Wood's maps go, the Boulder-clay occupies any level, irrespective 

 of inequality of surface, and therefore they prove that the hill and 

 valley system " was sketched out " before the deposit of the over- 

 lying Boulder-clay. Of course, in many places, the Boulder-clay 

 has been denuded by the present streams, and areas of London clay, 

 of variable extent, have been exposed. K Mr. Wood restricts the 

 term valley to the hollow in the immediate vicinity of a stream, 

 and does not mean the area below a line drawn from one water- 

 shed to another, he is merely disputing about terms. If the 

 excavation of the Thames Yalley, using the term in the latter sense, 

 took place in Post-glacial times, the deposits contained in it must also 

 be Post-glacial, and the evidence of fossils characteristic of Pliocene 

 mammals in France and Italy, is useless in classification. To say 

 the least, no evidence has yet been adduced in support of this 

 hypothesis, that is based merely on a belief that the entire valley- 

 system of the South-East of England originated in centres of arc-like 

 or curvilinear disturbance." W. Boyd Dawkins, 



11th November, 1867- 



DR. A. VON KOENEN, ON THE BELGIAN TERTIARIES. 

 To the Editor of the Geological Magazine. 



SiK, — In the November number of the Geological Magazine, M. 

 von Koenen, in dissenting from my way of viewing the Belgian and 

 East Anglian Kainozoic formations, represents me in a manner to 

 which I may reasonably object. My paper having been published in 

 the Journal of the Geological Society I should be sorry should its 

 members be misled. 



