1894. | NEW YORK ACADEMY OF SCIENCES. 179 
These deposits, old and new, are now generally described as 
‘* Lacustrine sedimentary,” but their exact age is a matter of 
constant discussion, because of the fact that almost every quiet 
body of water is to-day laying down a stratum of diatom shells 
of the same general character as that of the strata, which com- 
pose the relatively ancient and semi-fossil beds, which are found 
either dry or beneath existing lakes and ponds. As these beds 
are usually located in hollows, produced by glacial action, the 
earliest of them are doubtless to be referred to the Quaternary 
period (probably to the Champlain epoch). while the rest are of 
every possible age, down to the actually contemporaneous. — It 
is likely, however, that the process of deposition is at present 
proceeding at a much slower rate than that at which the earlier 
beds were formed, and this difference seems to be due, mainly, 
to a change of temperature, the climate towards the middie 
and close of the Champlain epoch being most favorable to dia- 
tom growth and multiplication. 
The extensive marine deposits of diatomaceous material in 
Maryland and Virginia, as well as the vast lacustrine and fluvia- 
tile strata of Nevada, Utah and other Western States, are proba- 
bly correctly referred to the Tertiary period. 
The fresh-water deposits of our Northern and Eastern States 
are divided into two classes, the sub-peat and the lacustrine 
proper. Deposits of the first-named class were laid down in 
bogs and marshes, or in bodies of water which subsequently 
became partially dried up, were then buried beneath gradually 
accumulating beds of vegetable debris, and were finally often 
grown over by trees and shrubs. Deposits of the second class, 
as a rule, were formed in ponds and lakes which have ever since 
continued to be such, or which were at some time suddenly 
drained by the destruction of their barriers or dams. 
In the specimen submitted to me I have thus far identified, as 
I think, eight genera and twenty-two species of what are known 
as free forms; but the individuals of these species are so ex- 
ceedingly numerous that they may be said to make up the great 
mass of the material. This fact leads to the conclusion that in the 
main the deposit was formed in a placid body of water. There 
are, however, to be found in it diatoms belonging to at least five 
genera and eight species which are either filamentous, stipitate 
or adnate in their methods of growth, which seems to indicate 
that a stream or streams flowed into or through the pond or bog 
from which the specimen came, by which these forms were intro- 
duced and mixed with the prevailing species. 
I have no information as to what proportion of ee five feet 
of peaty matter, which Prof. Hubbard says overlay the sticks 
