23 



mollusks. It will at once be admitted that they lived, like recent 

 oysters, upon Infusoria, and that they possessed the same beautiful 

 mechanism, though we cannot now detect it, for making a current of 

 food set in in the direction of their stomachs. The very structure, 

 then, of the oyster, independent of the result of any examination, de- 

 termines the fact of the cotemporaneous existence of Infusoria, and 

 their number may be approximately indicated by the countless bi- 

 valves themselves they were appointed to sustain. The supply would 

 be equal to the demand, and, moreover, of so vast an extent, that the 

 conclusion is unavoidable that the Kimmeridge clay, like the chalk, 

 is formed very largely of organic bodies, and is not the mere commi- 

 nuted detritus of more ancient and unorganized materials. 



The result of examination confirms this view. I find in the Kim- 

 meridge clay vast numbers of circular disks, already alluded to as ex- 

 isting in living oysters, and in addition to these I have met with 

 decided examples of the Coscinodiscus, and portions of calcareous 

 shells of Polythalamia. Under these circumstances we cannot fail to 

 suspect an absolute identity between the genera and species of some 

 of the 'minute and simple occupants of ancient and modern seas, 

 though larger forms of more complicated mechanism have successively 

 risen and disappeared. The oyster dissimilar from ours, may have 

 led upon our own Volvox, the Volvox on the Monad, and the Monad, 

 — but here we must pause, lost among the wonders of the ever-living 

 and life-giving Creator. 



From the nature of the present inquiry, it may be extended, theo- 

 retically at least, beyond the Kimmeridge clay. On the evidence of 

 analogy we may assume that the inhabitants of all bivalve shells, not 

 only in the secondary, but also in the seas of the transition formation, 

 were of similar habits to the acepalous mollusk which constructs the 

 oyster-shell; that being destitute of jaws, tongue, or mouth, the action 

 of a ciliary apparatus supplied them with food ; and that their food 

 consisted of an order of animals adapted, by their minuteness, to the 

 delicate mechanism of the cilia, and designed, by their multiplication 

 almost to infinity, to add mountain masses to the solid crust of the 

 earth. We may hereafter be indebted to the microscope for the con- 

 firmation of these views. 



I may embrace the present opportunity of further illustrating the 

 use of the microscope in geological researches, by making a passing 

 remark on the degree of heat to which the Kimmeridge clay has been 

 subjected. Microscopic crystals of carbonate of lime, which abound 

 in large portions of it, are either perfect cubes, or much nearer ap- 



