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 stratigraphic relations with the other beds, so 

 densely concealed is the surface by residual formations and vegetation, 

 I am convinced, from their geographic position and lithologic 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 the large and extensive coal bearing foi'mation 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. — I had almost completed my section of the 

 Isthmus, and despaired of determining the age of the Culebra clays, 

 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 



