120 Mr. J. F. Walker in reply to Mr. Seeley on the 
and vegetable matter till they increase to 100, you 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 imphed 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. Brodie’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 certain 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 1 is 
saturated with animal and vegetable matter. 
VI. Mr. Seeley repeats, “ with diffidence, on aecount 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. & VIL. 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 few others” to his remarkable state- 
ment about the species of Terebratule. 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 I-know, to the Portland Rock—very 
unlike Sowerby’s typical O. macroptera.’ Why does Mr. Seeley 
