HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 263 
sible to avoid the conclusion that the Tertiary sediments were derived 
from a near-by land which existed at the time of their deposition. Could 
they have been derived from some land which once existed to the north- 
ward in what is now the bosom of the Caribbean? In that direction we 
are confronted by great depths. If we turn to the South American 
continent as the source of this sedimentary débris we are again con- 
fronted by certain facts which oppose this hypothesis. Тһе narrow belt of 
country shows that the sediments derived from the ancient Andean and 
Venezuelan highlands in Tertiary time were deposited along its own 
coast. If we endeavor to argue that the westward flowing currents of 
the Caribbean could have distributed these sediments along the Isthmian 
region, then we must also acknowledge that there must have at the 
same time existed some littoral barrier against which they were de- 
posited. Turning to the Central American region lying to the west- 
ward, as a source of these sediments, we are confronted by the absence 
of any structural evidence of a watershed trending southward which 
could have deposited them over the Isthmian region. Тһе only hypoth- 
esis that can fit the condition of their present lay and arrangement is 
that they were derived from an adjacent land, and this land may have 
existed to the southward towards the Pacific coast, or in the area now 
covered by the Pacific waters of the Isthmian region, — a land which has 
disappeared as the land which once covered Panama Gulf is disappearing 
to-day. 
The fact that a series of marine sediments of Eocene and Oligocene 
Tertiary age at intervals fringes tho Caribbean coast from the San Juan 
at, Graytown, Nicaragua, to Cartagena on the northern coast of Colombia, 
and that these have been distorted and intruded by igneous rocks, by no 
means demonstrates that dry land did not exist toward the Pacifie side 
of the Isthmian region during the Eocene and Oligocene epochs of depo- 
sition. In fact, there are reasons to show that these sedimentations and 
disturbances may have taken place marginally against an older land 
during these epochs. 
We know beyond doubt that the Atlantic Tertiary sediments of the 
North American continent constitute a fringe which extends considerably 
inland from the present outline of the Atlantic Ocean as far south as the 
end of the Mexican Cordilleras. We also know that a very narrow rib- 
bon of Tertiary sediments borders the Pacific coast of California, but is 
only doubtfully represented to the south along the margins of Mexico 
to the Isthmus of Tehuantepec. Tt is known that these sediments of 
both coasts as far south as Tehuantepec were laid down against a 
