63 
geologist, receives new and unexpected illustration from these re- 
searches. Of about eighty species of fossil Infusoria which have 
been discovered in various strata, almost the half are species which 
still exist in the waters: and thus these forms of life, so long over- 
looked as invisible specks of brute matter, have a constancy and 
durability through the revolutions of the earth’s surface which is 
denied to animals of a more conspicuous size and organization. 
Again, we are so accustomed to receive new confirmations of our 
well-established geological doctrines, that the occurrence of such an 
event produces in us little surprise; but if this were not so, we could 
not avoid being struck with one feature of Prof. Ehrenberg’s dis- 
coveries ;—that while the microscopic contents of the more recent 
strata are all freshwater Infusoria, those of the chalk are bodies 
(Peridinium, Xanihidium, Fucoides,) which must, or at least can, 
live in the waters of the ocean. Nor has Prof. Ehrenberg been con- 
tent with examining the rocks in which these objects occur. During 
the last two years he has been pursuing a highly interesting series 
of researches with the view of ascertaining in what manner these 
vast masses of minute animals can have been accumulated. And 
the result of his inquiries is*, that these creatures exist at present in 
such abundance, under favourable circumstances, that the difficulty 
disappears. Inthe Public Garden at Berlin he found that workmen 
were employed for several days in removing in wheelbarrows masses 
which consisted entirely of fossil Infusoria. He produced from the 
living animals, in masses so large as to be expressed in pounds, tri- 
poli and polishing slate similar to the rocks from which he had ori- 
ginally obtained the remains of such animals; and he declares that 
a small rise in the price of tripoli would make it worth while to 
manufacture it from the living animals as an article of commerce. 
These results are only curious; but his speculations, founded upon 
these and similar facts, with respect to the formation of such rocks 
for example, polishing slate, the siliceous paste called hetselguhr, and 
the layers of flint in chalk, are replete with geological instruction. 
As the discoveries of Prof. Ehrenberg are thus full of interest for 
the geological speculator, so have they been the result, net of any 
fortunate chance, but of great attainments, knowledge, and labour. 
The author of them had made that most obscure and difficult portion 
* Abhandl. Kon. Ak. Wissensch. Berlin. 1838. 
