GEOLOGY AND PALEONTOLOGY OP THE CANAL ZONE. 527 



to be largely a product of running water. It is generally fairly well 

 bedded, though locally massive, and contains hard boulders, up to a 

 few feet in diameter, of andesitic, dioritic, and other igneous rocks. 



The upper part of this formation is of the same general composi- 

 tion as the lower part, but contains some beds of dark-gray clay marl 

 which contain fossil Foraminifera. The cobbles, boulders, and gravel 

 are from cherts, andesites, and diorites, and were derived from the 

 older intrusive masses of igneous rock now found at intervals along 

 the central part of the Isthmus. 



The formation must be at least 1,000 feet thick, and it outcrops 

 extensively in the vicinity of Bohio and near Caimito Junction. 

 Though not outcropping in the Gaillard Cut, it was encountered in 

 many of the cuts near Bohio on the new line of the Panama Railroad. 



CULEBRA FORMATION. 



The Culebra formation contains an upper and a lower member. 



The lower member consists of dark, well-laminated beds of soft 

 shales, marls, and carbonaceous clays, with some pebbly, sandy, and 

 tufaceous layers. There are a few thin beds of lignitic shale, but the 

 whole upper part of the formation contains considerable organic 

 matter. It outcrops in Gaillard Cut near Culebra and near Pedro 

 Miguel. 



The upper member consists of calcareous beds and lenses ranging 

 in character from sandy limestone to calcareous sandstone, 3 to 10 

 feet thick, separated by partings of dark carbonaceous clays and 

 fine-bedded tuffs. 



Locally this formation gives off a little natural gas and in some 

 small areas it shows slightly bituminous shales. 



CUCURACHA FORMATION. 



The Cucuracha formation is here described in considerable detail, 

 because in it not only the Cucuracha slide but also the big Culebra 

 slides developed. It is so named because of being the site of the 

 Cucuracha slide and because it is typically exposed near Cucuracha 

 village. 



The formation consists of a dark green, massive and locally bedded, 

 slightly indurated, volcanic clay rock of andesitic composition. It is 

 a land-deposited formation, overlying the marine Culebra formation, 

 from which it is separated by 10 to 20 feet of slightly indurated 

 gravel. It is the upper part of what Hill * and Howe 2 called the 

 Culebra formation. 



» Hill, R. T., Geological history of the Isthmus of Panama and portions of Costa Rica, Museum Com- 

 parative Zoology Harvard College Bull., vol. 28, 1898. 



s Howe, Ernest, Canal Commission Ann. Rept. 1907, Appendix E, pp. 108-138; Isthmian geology of the 

 Panama Canal, Econ. Geol., vol. 2, 1907, pp. 639-658; Geology of the Isthmus of Panama, Amer. Joum. 

 Sei., ser. 4, vol. 26, 1908, pp. 212-237. 



