180 
INTRODUCTION. 
suggestions we have alluded to deserve only the credit 
which is due to plausible conjectures. 1 
There is, however, a class of minor formations of the 
tertiary period, in which the testaceous remains point to 
more certain results. These we have mentioned as de- 
posited in the beds of lakes. When the body of water 
from which the deposit in these instances took place was 
small, it could of course only contain the productions of 
the lake itself, and of the region immediately around it. 
Hence species occurring together in such formations 
must have not only existed contemporaneously, but must 
have occupied the same geographical region, and have 
been subjected to the same physical influences. The 
inferences which may be drawn from them are therefore 
more to be relied upon. 
Shells of many of the terrestrial species, apparently 
in a fossilized condition, are often met with in collections, 
and are said to be brought from the western and south- 
western parts of the country. They indicate the exist- 
ence of the most recent tertiary or post tertiary forma- 
tions, but nothing certain is known of them. Dr. David 
D. Owen, of New Harmony, Indiana, has discovered an 
extensive deposit of this kind in Pusey county, on the 
This view of the subject is strongly corroborated by facts brought to 
light by the valuable researches of Professor Hitchcock. He has given to 
- ii. quivocal proofs of the existence of birds, in the must ancient mesozoic 
period through the evidence of their foot-tracks in the sandstone of the Con- 
necticul River valley. The number of species he has now made us ac- 
quainted with is not less than seventy, and y< t n< i| a single bone of any one 
of these ii - yet been discovered 
