HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 265 
The Culebra clay of supposedly Eocene age, which we have hypothet- 
ically correlated with the great coal formation of the Caribbean side of 
the Isthmian region, is the only sedimentary formation which occurs near 
the drainage divide of the oceans, and this is found only on the Carib- 
bean side, Тһе composition, structure, and fossils of these clays give 
no evidence of their deposition in a passage connecting the oceans, espe- 
cially a deep and extensive one. These clays are apparently entirely 
void of molluscan remains such as surely would have inhabited such a 
passage. In fact, their composition, made up so largely of land débris 
and plants, and their extensive distribution, are, in my opinion, сара- 
ble of but one interpretation, that, instead of indicating a free marine 
passage, they attest the existence of larger surrounding land areas in 
this region than now exist. 
Although the biologic and paleontologic evidence leads to the conclu- 
sion that a shallow connection did exist somewhere in Tropical America 
during Eocene time, neither the geologic nor the biological evidence 
shows conclusively that the Isthmus of Panama was the exact place of 
this connection. It merely proves that such a connection was probable 
somewhere in that vast Tropical region between the known localities 
of the Tejon beds in Lower California and the place of the occurrence 
of the Gatun beds on the Caribbean side near Colon. 
The occurrence ih the Tertiary of a few species common to the Atlan- 
tic and the Pacific have been reported by G. B. Harris as far northward 
as Galveston, Texas. A connection of the two oceans in Tertiary time 
in that latitude, from the well known evidence of the geological forma- 
tion and history, would be preposterous. 
The Oligocene and later faunas of the continental coast succeeding 
the Claiborne, so far as the writer is aware, are thoroughly Caribbean, and 
show no evidence of free commingling of species of the two oceans.! 
Harmony of Geologic Evidence with Biologic and Paleontologie Deduc- 
tions that Land Oonnection was thoroughly established during the Olose 
of the Miocene. — If the marine passage ever existed across the Isthmus 
or elsewhere in Tropical America, it must have been during the later 
Eocene epoch, for all evidence concerning later epochs shows that the 
great land barrier connecting the continents has existed since that. time, 
and that the seas have never since communicated across it. Hence the 
1 It has been alleged by several writers upon paleontology that Pacific forms — 
especially corals — do exist in the Miocene (Late Oligocene) fauna of the Great 
Antilles. We have proofs that many of the specific correlations were erroneous. 
This subject will be discussed in our report on Jamaica, 
