150' M. C. COOKE ON THE ESTIMATION OF 



man for ten years to count, even if he could count sixty per minute 

 for twelve hours daily. 



Ehrenberg calculated that there are one million and one third of 

 organisms in a cubic inch of chalk, and this is, without doubt, very 

 nearly correct. My block of chalk contains, roughly, about 216 

 cubic inches, and according to Ehrenberg* s calculation would con- 

 tain 288 millions of shells ; my calculation, derived by another 

 process, was 256 millions, and this was made before I was aware of 

 Frofessor Ehrenberg's computation, and serves to strengthen my 

 position, not only that I am below the actual number, but that I 

 am very near the correct number. If, therefore, I adhere to my 

 own calculation, it will be from a desire not to exaggerate. I must 

 think that these two independent calculations greatly strengthen 

 each other, and are enough to establish the fact that between one 

 million and a quarter and one million and a third of Foraminiferous 

 shells are contained in each cubic inch of Kentish Chalk. 



To communicate some idea of the vast number of shells contained 

 in one ounce of chalk, we will suppose that each shell were as large 

 as the shell of the common garden snail (Helix aspersd). If such 

 were the case, and these shells were placed side by side, then the 

 half million shells in one ounce of chalk would form an unbroken 

 line of twelve miles in length, or if we take the whole of the shells 

 contained in the lump I spoke of just now, and reckon them after 

 the same rate at 128 millions, then, if they were as large as snail 

 shells, and were placed in a line, that line of shells would be 3,072 

 miles in length, and would occupy an express train seventy-seven 

 hours to go from one end to the other, at the continuous rate of 

 forty miles an hour. 



It would be worse than folly to attempt any calculation of the 

 myriads of Foraminifera which are entombed in the chalk beds of 

 England alone, without reference to the similar beds in continental 

 Europe. The chalk pit from whence my specimens were derived 

 is situated at Swanscombe in Kent, and the present firm inform 

 me that, from this pit they have obtained more than half a million 

 tons of chalk, or 561,895 cubic yards. Figures would fail to con- 

 vey any idea of the number of Foraminifera which this single firm 

 has disturbed and removed from their last resting-place. These 

 minute shells would require 150 of most of them placed side by 

 side to extend over one-twelfth of an inch, and if we take the 

 commonest form — Glubigevina — the diameter of which is about 



