1879. ] Columbia College. SII 
had slowly attained this surpassing degree of elegance and orna- 
mentation, the whole family became extinct. The collection 
contains many of these chambered shells from the Cretaceous of 
the Upper Missouri, which still retain their nacreous walls, that 
after the lapse of ages are as beautifully iridescent as any living 
shell. Here also are the bones of some of the great reptiles of 
the Cretaceous, the teeth of fishes, and a great variety of shells 
and plants from the same rocks. Many of these specimens are 
of great scientific value, as they are the type-specimens upon 
which many of the genera and species of Cretaceous fossils were 
founded. 
The last case at the southern end of the geological hall con- 
tains the fossils of the Tertiary period, the last period but one be- 
fore the age of man. A glance at the contents of this case shows 
us that all the grand divisions of animals and plants which are 
living at the present day, are represented. The shells of this 
period exhibit a very modern aspect, especially when compared 
with the older ones we have been studying; although many cf 
them belong to living genera, yet nearly all the species are 
extinct. The tertiary plants, which are shown in great abundance, 
prove that the flora was not very different in its general character 
from that clothing the Middle States at the present day. The 
higher vertebrates at this time appeared in such numbers and 
variety that this age is known as the age of mammals. 
While lingering over the cases of Silurian fossils, we attempted 
briefly to retrace the picture of that age, with its small and barren 
land areas and its great oceans tenanted by the lowest forms of 
animals and plants. Let us contrast with the silent barren aspect 
of our continent in those primeval days, its appearance in Tertiary 
times. North America had then attained nearly its present out- 
line, althot extensive regions along the Atlantic and Gulf 
et beneath the ocean, and great lakes occupied the 
borders we y 
western interior. A flora of temperate or sub-tropical growth 
clothed the area of the United States, and the climate of Virginia 
reached as farnorthward as Greenland. The splendid collection of 
Tertiary plants from the region of the Upper Missouri, the Yel- 
lowstone, and other portions of the West, shows that the banks of 
the Tertiary lakes, which then existed at these localities but have 
since been filled, were fringed with a varied and beautiful vegeta- __ 
tion. We find among these fossil plants the leaves of the maple, — — 
t 
