120 Mr. J. F. Walker in reply to Mr. Seeley on the 



and vegetable matter till they increase to 100, yon will produce 

 a nodule of phosphate of lime." In return I may congratulate 

 him on having made a still more " notable discovery/' namely, 

 that clay consists of pure alumina, which is evidently implied in 

 his interpretation of my statements. Mr. Seeley ought to be 

 aware that clay consists not of alumina, but of a silicate of alu- 

 mina ; and also that clays like the Oxford and Kimmeridge 

 contain various other substances. Again, what Mr. Seeley 

 denominates " rolled concretions of tolerably pure phosphate of 

 lime " do not, in the best average samples, contain more than 

 22*39 per cent, of phosphoric acid=48"51 per cent, of tricalcic 

 phosphate, supposing it all combined with calcium (see analyses 

 given in Mr. JSrodie's paper). I hope at some future period to 

 demonstrate the origin of these nodules by chemical analysis. 

 The indication of the comparatively small amount of pure alu- 

 mina contained in clays may serve to a cei'tain extent to remove 

 Mr. Seeley's difficulty as to what " becomes of the clay ;" and I 

 may also remind him that, on his part, he has not told us 

 whence the alumina undoubtedly contained in the nodules is 

 derived. To Mr. Seeley^s objection to the word " soaked " I 

 can only reply that I used it to indicate my belief that the clay 

 derived from the sea-clifFs, formed of older beds, encloses and is 

 saturated with animal and vegetable matter. 



VI. Mr. Seeley repeats, " with diffidence, on account of the 

 state of the specimens,'^ that he gathered no extraneous fossils 

 from the bed. It is "on account of the state of the specimens" 

 that I regard them as derived from the denudation of older 

 formations. The condition of the bones and teeth of reptiles 

 and fishes shows that they have been rolled, and, moreover, rolled 

 after fossilization. 



VII. & VIII. Mr. Seeley complains that I did not take the 

 trouble to get the phosphatic casts of the shells named ; but he 

 cautiously omits to give a list of those which he has determined 

 to be Portland species ; he also omits a list of the ferruginous 

 shells. I gave a list of all I had obtained, when my paper was 

 published, that were in a condition sufficiently perfect for deter- 

 mination. 



IX. I am flattered by Mr, Seeley's remark that my list of 

 Mollusca has "some approach to correctness.'^ I am sorry that 

 he does not add the " some iew others " to his remarkable state- 

 ment about the species of Terebratulce. With regard to the 

 fossil I have named Ostrea macroptera, he makes the following 

 curious statement : — " Although this is the name used by me 

 for this fossil, as a variety of the O. frons of Parkinson, it is a 

 form limited, so far as 1 know, to the Portland Rock — very 

 unlike Sowerby's typical 0. macroptera." Why does Mr. Seeley 



