HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 199 



50 feet, and the length of the section is 200 feet.. The rock is appar- 

 ently stratified and shows pink, salmon, and magenta colors similar 

 to those seen in the Potomac formation of the Eastern United States. 

 The material resembles a fine light grained clay sandstone, but is singu- 

 larly free from grit. These rocks are indurated on the surface, and 

 strongly oxidized. No traces of fossils could be found. There are 

 sti-ong synclinal and anticlinal folds cut by vertical faults, showing clearly 

 that the rock has been subjected to serious displacement since its for- 

 mation. This outcrop is important, inasmuch as it is on the flanks of 

 the Pacific side of the great igneous masses of the Isthmus, and, as will 

 be later shown, has a strong and suggestive relation to the Barbacoas 

 formation of the Atlantic side. (See Panama Formation, page 200.) 



The Panama Swamp Levels. — Past the outcrop at Miraflores the 

 road descends into the old alluvial sedimentary level valley or swamps 

 of the Eio Grande, above the level of which project at various intervals 

 hills of igneous rocks. These swamp levels are singularly like those of 

 the Caribbean side, and are irregular indentations into the rugged coast 

 topography. 



The swamp lands lie on all except the ocean side of the Cerro Angon, 

 a great rounded mountain, estimated to be 600 feet high, against the 

 foot of which the city of Panama is built. Maack notes the occurrence 

 of recent shells in these swamp lands at numerous places around Panama, 

 coextensive with their extent, which shows that they, like the Caribbean 

 swamps, are elevated marine sediments rather than recently base levelled 

 plains. 



Between Rio Grande (43 miles) and Carosal (44.17 miles) other small 

 hills of decomposing basalt rise above the swamp level of the Rio Grande 

 bottom. 



From Carosal on to Panama the road follows the wide flat swamp 

 level plain or playa, surrounded by the Culebra hills on the east and 

 north, and the great Cerro Anqon upon the west, around the north end 

 of which the Rio Grande is deflected, reaching the Pacific about three 

 miles west of the city. 



The Cerro Angon. — This peculiar isolated eminence, separated by 

 the Rio Grande swamp level from the Culebra group of summits, 

 certainly presents a topographic aspect far different from that of 

 any other summit seen by me in the region, its less pointed and more 

 rounded mam miliary shape being in strong contrast with the peaked 

 summits of both the mainland and adjacent islands elsewhere seen, 

 and strongly suggests that it is of a different composition, not only 



