Correspondence — Mr. A. F. Griffith. 383 



provisionally drawn ; and until some reason is given, I think the 

 Leda myalls Bed may be left with the Crag. A land surface, as we 

 know from the Purbecks and Coal-measures, does not necessarily 

 mark a break in the series. 



While agreeing with Mr. Blake that the term " Forest Bed " is a 

 misnomer, the suggested alteration to " Rootlet Bed " seems a good 

 deal worse. As well might we class together the London and 

 Oxford Clays, because at the present day the roots of the same 

 species of trees penetrate both. The rootlets of the Forest Bed 

 penetrate whatever happens to be underneath them ; sometimes the 

 Weybourn Crag, sometimes higher beds. Even if names are not 

 quite correct, it is better to accept them with a slightly altered mean- 

 ing than to upset all our nomenclature for every fresh theory. 

 Therefore I think the name "Cromer Forest Bed," having now been 

 in use for over 50 years, ought not be changed, but should be ac- 

 cepted with the meaning that it consists of a series of sub-aerial, 

 lacustrine, and estuarine beds formed in, and from the debris of, a 

 forest-clad country. 



Mr. Blake uses the name '•' Bure Valley Beds " for what was 

 termed the Leda mi/alis Bed ; but I have already shown that Messrs. 

 Wood and Harmer's typical Bure Valley fauna comes from the Wey- 

 bourn Crag beneath, instead of above, the Forest Bed,^ while at present 

 the Leda myalis Bed has not been recognized in the Bure Valley. 

 The test of thickness is of no value in these shallow- water beds ; 

 for after they have once reached the sea-level, they may remain for 

 an indefinite time without either erosion or deposit. In our British 

 Pliocene beds it should be remembered we have only the feather 

 edge of a formation, which must be much thicker where the water 

 was sufficiently deep, and perhaps might equal the 700 or 800 feet 

 of the Sicilian Newer Pliocenes. I am astonished at Mr. Blake's 

 statement that the thickness of the beds between the Cromer Till 

 and the Chalk never exceeds 30 feet ; the average measured thickness 

 exceeds that amount, and at Happisburgh I have reason to believe 

 that the Forest Bed alone is more than 60 feet, for I have dredged 

 and found it in place in 10 fathoms near the shore, and it extends 

 upwards to high water. Clement Eeid. 



Hornsea, Hull, Qth June, 1881. 



OBLIQUE AND ORTHOGONAL SECTIONS. 



Sir, — If Mr. Day will examine the figure given with his letter 

 in the March Number of this Magazine, he will perceive that Mr. 

 Fisher's ' cavils ' are well founded. Not only has Mr. Day inter- 

 changed the symbols a and ^, but his angle </) has no connexion 

 whatever with anything in Mr. Fisher's paper. Mr. Fisher might 

 no doubt have given a simpler proof of each of his equations (2) and 

 (3) by the method indicated by Mr. Day, but one figure would not 

 then have sufficed for the whole proof. 



Mr. Day's suggestion of casting a shadow in sunlight, in order to 

 find the form of outcrop, is, as Mr. Fisher I'eadily admits, useful, but 

 he does not tell us how to carry out the inverse process, viz., given 

 1 See Geol. Mag. Dec. II. Vol. IV. p. 300 ; and Vol. VII. p. 548. 



