THE 



GEOLOGICAL MAGAZINE. 



No. XXXV.— MAY, 1867. 



OS/IG-IIsrJLIj J^E/TIOIjES- 



I. — On the Ages of the "Trail" and "Wakp." 

 By the Eev. 0. Fisher, M.A., F.G.S. 



HEEE are some points in Mr. Maw's ^ article on the relative 

 ages of the Boulder-clays^ which require notice from me, be- 

 cause they involve the consequence of assigning to the deposit which 

 I have described under the name of " trail" an antiquity far higher 

 than that which I believe to belong to it. 



Mr. Dawkins, in his paper on the Brick-earths of the Thames 

 valley,^ noticed this deposit as being seen in all the sections he de- 

 scribed; and he agreed with me in believing it to be a Glacial 

 deposit, and, as I understood him, a subaerial one. In these views 

 he corroborated my conclusions, as will be seen by reference to my 

 papers on the subject in the Quarterly Journal, and this Magazine.^ 



Mr. Maw, however, endeavours to show a probability that the 

 Glacial deposit of the Thames valley is co-ordinate with the Boulder- 

 clay, or till, of the Norfolk coast ; and gives reasons for supposing 

 that the latter is more recent than the Boulder-clay capping the 

 higher ground of the Eastern Counties. With regard to this second 

 qxxestion, I have nothing to say at present, but I demur entirely to 

 the position that the Glacial deposit overlying the Brick-earth is of 

 the age of the Norfolk till. Mr. Dawkins, if I recollect rightly, put 

 forward the idea that we might have in the Thames valley a remnant 

 of a subaerial deposit of the age of the true Boulder-clay. This was, 

 as Mr. Maw says, objected to during the discussion on the ground 

 that the Thames valley was newer than, or at any rate deepened 

 after, the period of the Boulder-clay. But I went further, and said 

 that I recognized in the apparently Glacial deposit capping the 

 Brick-earths at Ilford and Grays Thurrock the same deposit which 

 I have noticed and described as filling troughs in the general surface 

 of the country, and consisting of materials transported from higher 

 groimds in rear by some agent, which I believe to have been land 

 ice. This deposit, which I call "trail," whatever its origin may be, 

 is evidently connected with the last denudation of the surface, 



1 See Geological Magazine for March last, p. 97. 



2 Kead at the Geological Society, 9th January, 1867. 



3 Journal, vol. xxii. p. 554, and Geological Magazine, vol. iii. p. 483. 



VOL. IV. — NO. XXXV. 13 



