HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 199 
50 fect, 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 
strong 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 Rio 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 Angon 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 mammillary 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 
