MACKIE — THOUGHTS ON DOVER CLIFFS. 
285 
while these parasites lived, grew, and died before they were embedded 
in the slowly accumulating mud. 
In my former collection, now the property of the town of Folke- 
stone, there is a fossil oyster — by no means an uncommon example — 
having a second oyster attached to the inside of one valve. This 
specimen could neither have been suddenly enveloped nor even em- 
bedded shortly after death. Decomposition and entire disappearance 
of the animal must have taken place before the smaller oyster could 
have fixed its residence. This too must have died, and the connect- 
ing ligament of its valves have decayed, before the detached valve 
was worked away, and both oysters, old and young, embedded to- 
gether. 
Of all the numerous specimens of the prickly sea-urchin tribe from 
the Cretaceous rocks, to find one with any of the spines attaclied is 
rare, while the test itself is often coated with Serpulje and other para- 
sitic forms. In such cases also, not only death and the subsequent 
decomposition of the muscular integument must have happened, but 
the spine-divested body-shells of the Echiuoderms must have remained 
exposed on the sea-bottom, while these extraneous beings lived out 
the full periods of their existences. 
The extremely slow formation of the Chalk is further displayed in 
its microscopic structure. 
Amongst all the wonders which geology has revealed, there is no- 
thing perhaps more wonderful than that the very substance of solid 
rocks should be composed of the remains of the minutest animalcules. 
Tet such the microscope has shown ; and chalk is one of the nume- 
rous instances. 
Every atom, each individual particle, was once part of a living crea- 
ture. Thousands of miles of solid rock, hundreds of feet in thickness, 
form thus a mighty tumulus of fragile invisible beings, — the cemetery 
of the unseen; beings not suddenly nor violently destroyed, but 
that naturally sported awny their lives above the dead ones of their 
race, a million of whose carcases scarcely formed a cubic inch of the 
Cretaceous ocean's mud. 
Beautifully and truly has it been said, that "the majesty of God 
appeareth not less in small things than in great, and as it exceedeth 
human sense in the immensity of the Universe, so doth it also in 
the smalluess of the parts thereof." The deposits of the Cretaceous 
period are very extensive, and are found in Belgium, Holland, Prussia, 
and over the greatest portion of Europe. A map of the divisional 
