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University of California. 



[Vol. 2. 



and the peculiar breccia beds and breccia conglomerates so charac- 

 teristic a feature of the Santiago formation. 



Finally another orographic disturbance again folded the strata 

 of the southern half of the Peninsula of Azuero into a mountain 

 system, tilting the Santiago formation almost to a vertical position. 

 Associated with this movement was an uplift of the sea-bottom on 

 the north of the "old land" and an extension of its limits to at 

 least the northern edge of the Aguadulce-Santiago plain. During 

 the following short epoch of sub-aerial erosion, broad shallow 

 basin valleys were eroded in the surface of the Santiago formation. 

 Early in the Eocene period, the plain was submerged and the 

 Tertiary basal conglomerate and overlying red shale were deposited 

 on its surface. The evidence is very clear that the material was 

 derived from the south. Indeed, I think the "old land" still 

 remained in large part above sea-level, and its red residuary soil 

 furnished the material for the lower Eocene formations. 



Now a radical disturbance of the quiet of this land was inaugu- 

 rated. Far out in the sea, at the edge of the sub-marine shelf 

 which bounded the "old land" on the north, was a line of weak- 

 ness. Here the earth was fissured along an east-west belt on the 

 site of what is now the southern foot-hills belt of the Cordillera 

 de Veraguas and extending thence east over the site of Panama. 

 Lava and ashes issued from volcanic vents, the latter to be largely 

 deposited in the shallow sea between the volcanic range and the 

 old land. At first the material was very acid, but later came 

 highly basic eruptions. A broad strip was added to the old land 

 merely by the accumulation of igneous debris. Then came an 

 epoch of quiescence, during which the fossiliferous late Eocene and 

 early Miocene sedimentaries were deposited in the sea on the north 

 side of the volcanic range. 



The next event was the profoundest disturbance of which we 

 have a record, that has ever affected any part of the Isthmian 

 country. This was the upthrust of the Cordillera de Veraguas to 

 a high mountain range, and the invasion of the volcanic series by 

 huge batholites of alkaline granite and syenite. The old Andean 

 system of orographic disturbances had ceased and instead had 

 come into action, as Mr. Hill has indicated, the Antillean system. 



