480 Correspondence. 



degree erroneous. Some modifications — not affecting, however, the 

 main points of structure — I perceive^ will have to be made, especially 

 the absence of the Middle Glacial sands in the north-west part of 

 central Norfolk, and the presence there of extensive Post-glacial 

 gravels ; and I think it not improbable that the Till of Cromer, 

 which in the structural section given by me in the 22nd volume of 

 the Quarterly Journal of the Geological Society, is shown as occupying 

 the same position of inferiority to the contorted drift as that pos- 

 sessed by the Chillesford clay, although necessarily for want of 

 connexion along the line of section distinguished by a separate letter, 

 may prove to be an expansion of that clay itself. It is a step, 

 however, gained, that one point, for which I have long contended, is 

 now admitted to be correct by my principal opponent,^ viz. the 

 superiority of the Chillesford shell-bed to the Fluvio-marine Crag ; 

 and that the identity which I pointed out between this bed and the 

 Upper Crag of Mr. Taylor, has now received the assent of Mr. 

 Taylor, Mr. Gunn, and Mr. Maw. 



Perhaps you will permit me to observe, in reference to Mr. Daw- 

 kins' letter respecting the Boulder-clay of Havering, that if by the 

 phrase, " on the southern side of the range of heights that form 

 the northern boundary of the Thames Valley," he means to imply 

 that the Boulder-clay lies in the valley of the Thames, I demur 

 wholly to such an implication. The patch at Havering (as Mr. 

 Dawkins knows) is shown in my survey map, placed in the library 

 of the Geological Society, and its position illustrated by section.^ It 

 may be seen from the map and sections that the heights of the 

 north side of the Thames Valley are formed of Bagshot sand and 

 Boulder-clay together (the latter having taken the place of the 

 former, and of the uppermost part of the London clay), and that the 

 northern valley slope has been cut down from these two formations 

 indifferently ; so that, instead of the Boulder-clay at Havering lying 

 on the southern side of the heights, it is essentially a part of those 

 heights themselves. — I am, Sir, your obedient servant, 



Seakles V. Wood, Jun. 



BEITISH FOSSIL CORALS. 

 To the Editor of the Geological Magazine. 



Deak Sm, — The generic name of the Carboniferous corals, formerly 

 confounded with Aulophyllum, should be Oyclophyllum, not Cyclocyathus 

 (see Geol. Mag., September, 1867, p. 416). There is an error in 

 my monograph of the Liassic Corals, which makes Trochocyathus 

 Moorei, Ed. and H., stand in the place of Thecocyathus Moorei, 

 Ed. and H. As these errors may give rise to much bewilderment 

 will you kindly insert this note. Yours truly 



P. Martin Duncan. 

 September 18th, 1867. 



1 Fisher, Quar. Journ. Geol. Soc, Vol. xxiii. p. 175. 



2 See also Section No. 4 of ray paper in the forthcoming numher of the Quarterly 

 Journal of the Geological Society, and Vol. III. p. 57, of the Geological Magazine. 



