50 Dr. Wallich on the Identity of the Chalk 
Greensand) at Folkestone, but, most abundantly, in Grey 
Chalk from the Finchley Boulder-clay.” 
Mr. Young, knowing the interest taken by me in the 
matter, was good enough to acquaint me with his discovery 
soon after making it im April last, and to increase the obli- 
gation thus rendered, by presenting me with illustrative slides 
and specimens of the Chalk itself, intimating at the same time 
that I was at liberty to make any use I liked of the informa- 
tion. He thus enabled me not only at once to verify his 
observations, and, under the salutary stimulus afforded by his 
discovery, to detect coccospheres in two or three specimens of 
chalk I had by me, but, what was of still greater interest to 
me just now, owing to its opportuneness, to detect selicified 
coccospheres in the cavities of hermetically closed nodules ob- 
tained direct from the Upper Chalk, and also in a number of 
similarly closed hollow flints obtained, in the usual rolled and 
weathered condition, from neighbouring gravel beds! 
It is at this point that the history of these still myste- 
rious little structures becomes so intimately connected with 
the flint question as to warrant my laying greater stress on it 
than I should otherwise have done; for not only does it add 
another powerful link to the chain of evidence regarding the 
mineral identity of the chalk and recent calcareous deposits, 
but it conclusively attests the accuracy of the statement made 
by me when I first figured and minutely described the cocco- 
spheres *—namely, that, in common with the detached appen- 
dages of these organisms called ‘ coccoliths,” the cell-wall of 
the coccosphere ts consolidated by carbonate of lime tT, and hence, 
when not silicified, exhibits by polarized light the well-known 
distinctive cross. I may take this opportunity of mentioning 
that, as some doubts have been expressed as to the correctness 
of my view regarding the calcareous nature of the cell-wall 
of the structures in question, I have during the past twelve 
months carefully repeated my examination of them, and am 
now in a position to reassert its strict accuracy in every par- 
ticular. 
I have spoken of the lithological identity of the ancient 
* “On some novel Phases of Organic Life at Great Depths in the 
Ocean,” Ann. & Mag. Nat. Hist., July 1861. 
+ It is a remarkable fact, also pointed out in the paper just named, that 
T had never then (and I may here add that I have never since, either 
during my cruise in the North Atlantic in 1860 or during my subsequent 
examination of preserved specimens) observed a single collapsed or 
crumpled specimen. In the large oblong coccospheres found by me, in 
1857, in the tropical ocean on both sides of Africa, one end of the struec- 
ture “dehisces,” as if truncated ; but I do not recollect having ever seen 
it crushed or collapsed. 
