2 
GEOLOGY 
At Barbacoas, the bank of tbe river is high and formed of stratified rocks. They form a bluff 
about one hundred feet in elevation, and the bedding is distinct. The strata, apparently, 
dip to the west at an angle of five degrees, and the trend is north and south. The strata are 
argillaceous sandstone, and have a grayish green color. 
Barbacoas to Cruces .—We took boats at the foot of this sandstone bluff and proceeded up the 
river. The banks for nearly the entire distance were completely hid by the dense and beautiful 
tropical foliage, so that the rocks were not visible. The river terrace, or bank, appeared to vary 
from ten to twenty feet in height. Some large boulders, or drift-rocks, were seen on a high 
hill, where a cutting for the railroad was made. At Gorgona, the beach pebbles were princi¬ 
pally trappean and basaltic, with some agates. A bank of conglomerate, with some large 
boulders, was also seen. At Cruces, similar pebbles and boulders, or a coarse river-drift, was 
found, some of the rounded masses being over a foot in diameter. This place is near the base 
of the high mountains. 
Cruces to Panama , June 17.—Disembarking at Cruces, at 10 P. M., we remained over-night, 
and in the morning mounted mules for Panama. Soon after leaving the town, the path led 
through a narrow defile in a soft rock, which appeared to be similar to that seen at Barbacoas ; 
but it was so much overgrown with green moss, and covered with mud, that its character could 
not be determined. The path, however, was only wide enough for a mule to squeeze through ; 
and it appeared to have been worn down by the feet of animals alone, as there were deep foot- 
holes at regular distances. From this place to Panama very few observations on the rocks could 
be made. They were obscured by vegetation beyond the path; and along it the only formation 
visible was a deep, semi-fluid, red and black mud. The highest part of the route, however, 
(the summit of the mountains of the Isthmus,) appeared to be formed of compact greenstone. 
The paving-stones, also, which were used to construct the old road in the time of the bucca¬ 
neers, appear to be of basalt and greenstone. Indeed, at one point, near the western base of 
the mountains, I observed a rock decomposing and breaking up into globular masses, like some 
of the trappean and trachytic rocks. The city of Panama is built directly upon the shore of the 
bay, and it is underlaid by nearly horizontal strata of a red sandstone, which much resembles 
some portions of that in the Connecticut river valley. It is regularly stratified, as can be seen 
at many points about the shore, at low tide ; and the edges of the beds rise in succession over a 
wide surface, which is left uncovered by the water. The strata dip southward at an angle of 
about five degrees, and they are composed of alternate layers of compact red sandstone and 
light colored shales. The layers of the sandstone will average fifteen inches in thickness, and 
the shales six to ten. The gentle dip of the strata permits broad surfaces of each layer to be 
exposed to view; and when the tide is out the formation can be conveniently examined. Several 
specimens of the rock, containing remains of vegetation converted to lignite, were obtained. 
The surface of the rock was also marked in many places by curious figures, in relief, resembling 
roots of plants ; and one, nearly two feet in diameter, had the form of specimens of Comatula. 
No fossil shells could be found; but this sandstone is probably Tertiary. It is used in the con¬ 
struction of walls in the city, and the old fort is built of it. The stones of the walls are much 
worn away by the weather, and present the curious appearance of being hollowed out towards 
the centre, the mortar of the joints not weathering so rapidly as the rock. 
Panama to San Francisco .—We left Panama on the 20th of June, in the steamer California, 
Captain Whiting. The high hills and mountains, covered by dense tropical vegetation to their 
summits, with the towers and ruins of the city at their base, presented a beautiful appearance as 
