Doll's Tertiary Fauna of I'loriila. — Schiic/u-rt. 149 
from llicni, llic conclusion that tliis i)ortion of the boreal lignite-bearing 
rocks should bo regarded as Oligocene is irresistible. 
"The marine Oligocene sediments of the southern coast arc at first 
characterized by the appearance of vast numbers of foraminitera, the 
species in some cases identical with European forms referred to ap- 
proximately the same relative place in the Tertiary column. The organic 
limestones characterized by the presence of myriads of Orbitoidcs reach 
a remarkable thickness; the mass of this limestone, which forms the 
substructure of the Floridan peninsula, has been drilled to a depth of 
more than two thousand feet without definitely reaching the subjacent 
Eocene. Towards the end of this sedimentation Nummulites make their 
appearance for the first time in our Tertiary, and the echinoid fauna is 
so similar to some of that in the European Oligocene as to lead various 
geologists to the conclusion that a continuous coast or belt of islands 
must have extended from the Mediterranean region to the Antilles The 
thickness and extent of the Vicksburg limestone, stretching from the 
Floridian region to Costa Rica, and its singular absence from the Antil- 
les, so far as yet identified, taken together with the comparative thin- 
ness of the post-nummulitic Oligocene on the Gulf coast and its enorm- 
ous development in the Antillean region, the north shore of South Amer- 
ica, and the region of Middle America south of Mexico, suggest that 
during the period indicated there was at first a depression of the conti- 
nental border coincident with elevation of Antillean lands, while during 
the period of the upper Oligocene these conditions were reversed, the 
continental sea margin being brought near to, and even, at the Ocala 
islands, above the surface of the sea, while a depression of Antillean 
lands and Middle America permitted the formation of those great bodies 
of marine limestones and marls for which the upper Oligocene of those 
regions is so remarkable. As in Europe so in America, lake-beds were 
formed away from the seacoast, where the bones of Oligocene verte- 
brates were entombed to serve in the future as convincing evidence of 
contemporaneous evolution. Again, as in Europe, those changes which 
elevated the Alps terminated the processes assigned to Oligocene time ; 
so in America the Middle American highlands, the larger Antillean 
islands, and the peninsular island of Florida were uplifted, the two 
•Americas united, and vast physical changes consummated. Coincident- 
ly at the north the boreal coasts were gently depressed and the waters 
of the Miocene sea extended over the ruins of the Oligocene forests. 
"As indicated by the changes in the fauna, the physical changes at- 
tending the close of the Oligocene were at first slow, allowing a certain 
element of transition to appear in the Oak Grove or uppermost Oligo- 
cene fauna. At the last they appear to have been sudden, at least the 
change in the fauna on the Gulf coast was absolute and complete. The 
change was not only in the species and prevalent genera of the fauna, 
but a change from a subtropical to a cool temperate association of ani- 
mals. Previously, since the beginning of the Eocene, on the Gulf coast 
the assemblage of genera in the successive faunas uniformly indicates a 
warm or subtropical temperature of water, and the sediments uniformly 
