THE GEOLOGIST. 
90 
We figure a shell from the white chaJk, one valve of an oyster 
■with another smaller one attached to the internal surface. The 
first oyster must have hved and died, its animal substance must 
have been decomposed, or have been eaten out by the scavengers of 
the deep, ere the second could have attached itself to the inner surface 
of its valve, and this smaller one must have lived and grown from 
its almost microscopic state of fry to the size of the second oyster 
probably of two years' growth — for the oysters of the chalk are small 
and thin. Suppose this : then it must have taken more than two 
years before the slowly-falling sediments of the Cretaceous Sea had 
accumulated to the extent of a few stout sheets of paper. Now 
the ordinary aggregate thickness of the three associated chalks, 
upper and lower white, and grey, is not much less than a thou- 
sand feet, and all this mass was formed at no greater maximum rate. 
The fossil shells and fish we find imbedded in its strata, of course 
lived and died in its waters — they were living-beings in those 
remote days. So self-evident does this fact seem, — although it was 
once stoutly discussed — that I have not dwelt upon it, nor shall I, 
as any doubts on this point will be swept away in the natural 
progress of our remarks. And yet the chalk is itself but a 
portion of the Cretaceous group or system of rocks, and that 
system but one amongst many systems formed at no quicker rate. 
("To be continued J 
FOREIGN CORRESPONDENCE. 
By Dr. T. L. Phipson, of Paris. 
Late Mortality amongst distinguished Geologists — Action of Water on 
Plutonic Rocks — Artificial Production of Minerals ; A ragonite formed 
in Steam Engines ; Rubies and Sapphires — Oscillation of the North 
and South Coasts of France — The Sand of the Desert of Sahara — 
Tlie Coryphodon — Newly discovered Foot prints of Extinct Animals — 
Researches on the Flora of the Tertiary Formations. 
Before entering upon the regular correspondence with which we 
hope to entertain our readers each successive month, by making 
known to them every new and important geological fact as it comes 
