and Recent Calcareous Deposits. 49 
on the presence, or exhaustion, of the water of the ancient 
ocean which was imprisoned along with the solid materials. 
It is upon the exhaustion of this water that each one of the 
various transitional stages of metamorphism in the materials 
—ranging from a partial replacement of the carbonate of lime 
by silica, to the production of a form of chert so homogeneous 
and white as closely to resemble porcelain—is brought to a 
final standstill; whilst between these two extremes is to be 
met with every intermediate stage of (what I may describe as) 
collateral metamorphism, including the production of chalce- | 
dony or jasper through an occasional excess of alumina and 
iron, of fibrous as well as granular silica, and, finally, of the 
purest crystals of quartz, crystallized out of the last expiring 
remnant of water holding in solution the last residuary particles 
of silica. 
Of each and all of these transitional varieties of the material 
I have preserved representative specimens; and it is no exag- 
geration to say that each time I look at them some new fact 
seems to reveal itself in their wondrous history. 
On the present occasion I will content myself with drawing 
attention to two of the facts that have been elicited. The 
first is, that in those nodular cavities in which the imprisoned 
contents have not already been reduced to an anhydrous con- 
dition—putting one in mind of our satellite the moon, without 
atmosphere, without vapour, without even a ray of the 
reflected light she receives—the whole of the changes above 
enumerated can be distinctly noted as being either still in 
progress or as having been cut short by the exhaustion of the 
water, to which alluusion has just been made. 
The circumstances connected with the second fact on which 
I propose to touch, demand a few words of explanation. This 
_ I have all the more pleasure in supplying, since it enables 
me to make the interesting announcement, that the still 
mysterious little organisms to which I gave the name of cocco- 
spheres (discovered by me in 1860, amongst the rest of the 
organic débris*, in soundings in the North Atlantic), have very 
recently, and for the first time, been detected by Mr. J. T. 
Young in a fossil state. Mr. Young has already detected 
them in the Chalk series from various localities in the neigh- 
bourhood of London. They have, up to this date, been found 
by him “in the Chalk from Marlow, Pinckney’s Farm (near 
Maidenhead), Charlton, Gravesend, the Grey Chalk from the 
boring at Meux’s brewery, and the Glauconite beds (Upper 
* As stated in a paper on the Polycystina in the Quart. Journ. Micro- 
scop. Soc, for July 1865, I discovered living coccospheres in abundance 
in the tropical seas on both sides of Africa in 1857. 
Ann. & Mag. N. Hist. Ser. 5. Vol. viii. 4 
