HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 195 
pebble interbedded with the clays themselves in the lowest cuts is also 
evidence that some of the igneous mass existed during the deposition of 
these clays. 
I was able to trace the Culebra clays as far north on the railroad line 
as Gorgona, and as far south as the Pacific end of the Culebra Pass, in 
which direction they abruptly end. Nowhere, however, could I find a 
contact showing their stratigraphie relations with the other beds, so 
densely concealed is the surface by residual formations and vegetation, 
I am convinced, from their geographic position and lithologie resemblance, 
that they belong to the Eocene Tertiary formations of the Isthmus and 
near the base of that group. I am also inclined to believe that this is 
part of tho large and extensive coal bearing formation which has been 
found at many places throughout the entire Isthmian region. These 
clays certainly extend north to Las Cascadas, where they have exposed 
a thickness of 150 feet, and where they are again broken through by the 
Obispo massives. I was informed that similar clays containing coal 
deposit also occur back of Frijoles Station. 
The Empire Limestone. — 1 had almost completed my section of the 
Isthmus, and despaired of determining the age of the Culebra olays, 
when my attention was called to an old lime kiln about two miles north 
of the Culebra Summit near Empire Station (miles 34.5), where some 
Italians in former years had erected a lime kiln and burned limestone 
from the vicinity. This locality was seen and described by Maack. It 
is almost at the crest of the Culebra Pass, occurring less than two miles 
north of the so called continental divide, and surrounded for miles on 
each side by igneous rocks and the clays of the Culebra basin. Mr. 
Cunningham, Chief Engineer of the railroad, kindly accompanied me to 
the locality, and we succeeded in finding the ancient kiln, and a small 
outcrop of the undoubted limestone, massive, semi-crystalline, and yel- 
low-white in color, resembling somewhat the harder limestones of the 
older Tertiary of the Antilles. Only two small areas of this formation 
were exposed, in the cutting on the west side of the track, about 10 vertical 
feet, and below it toward a little creek a small knoll about 20 feet in 
diameter. The 10 feet of this limestone exposed in the cut added to 
that of the lower lying mound would indicate at least 50 feet in thick- 
ness of the formation. The outcrops show slight angles of inclination 
and jointing, such as would suggest considerable disturbance. The con- 
tacts and relations to all other rocks were so obscured by the thick red 
clays and vegetation that it was absolutely impossible to trace its extent 
away from the outcrops. In the creek bottom. about 75 feet below the 
