MICROSCOPIC CHAMBERED SHELLS. 117 
tacea and of larger animals, minute examination 
discloses occasionally prodigious accumulations 
of microscopic shells that surprise us no less by 
their abundance than their extreme minuteness ; 
the mode in which they are sometimes crowded 
together, may be estimated from the fact that 
Soldani collected from less than an ounce and a 
half of stone found in the hills of Casciana, in 
Tuscany, 10,454 microscopic chambered shells. 
The rest of the stone was composed of fragments 
of shells, of minute spines of Echini, and of a 
sparry calcareous matter. 
Of several species of these shells, four or five 
hundred weigh but a single grain ; of one 
species he calculates that a thousand individuals 
would scarcely weigh one grain. (Saggio Orit- 
tografico, 1780, pag. 103, Tab. III. fig. 22, H. 1.) 
He further states that some idea of their dimi- 
nutive size may be formed from the circumstance 
that immense numbers of them pass through 
a paper in which holes have been pricked with 
a needle of the smallest size. 
Our mental, like our visual faculties, begin 
rapidly to fail us when we attempt to compre- 
hend the infinity of littleness towards which we 
are thus conducted, on approaching the smaller 
extremes of creation. 
Similar accumulations of microscopic shells 
have been observed also in various sedimentary 
deposits of freshwater formation. A striking 
