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 1 In that direction we 

 are confronted by great depths. If we turn to the South American 

 continent as the source of this sedimentary debris we are again con- 

 fronted by certain facts which oppose this hypothesis. The 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. The 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 the Caribbean coast from the San Juan 

 at Gray town, 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 Pacific 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. It is known that these sediments of 

 both coasts as far south as Tehuantepec were laid down against a 



