GEOLOGIC SECTION OF PANAMA CANAL ZONE 709 



stone to calcareous sandstone, 3 to 10 feet thick, separated by partings of 

 carbonaceous clays and fine-bedded tuffs. This formation seems to be at least 

 500 feet thick. 



Number 5. Cucuracha Formation 



The Cucuracha formation consists of greenish, fine-grained clay, with some 

 local Red Beds. It is fairly massive, but contains a few beds of lignitic shale, 

 some lenses of gravel, sandy beds, and one extensive flow of gray andesitic 

 lava about 20 feet thick. It outcrops along the canal near Rio Grande and on 

 both sides of Gold and Contractors hills. Its chemical composition is ande- 

 sitic, it is cut by some basalt dikes, and is about 400 feet thick. 



Number G. Emperador Limestone 



The Emperador limestone lies unconformably on several of the older beds. 

 It is a light-colored, fairly pure limestone, which contains many corals, some 

 pelecypods, and other marine fossils. Its outcrops are somewhat flaggy and 

 occupy comparatively small areas. Near Las Cascades a section cut by the 

 canal shows five distinct beds, some of which are marly sandstone. The lower 

 beds are 4 to 6 feet and the upper one about 25 feet thick. The formation 

 outcrops northwest of Empire, south of Las Cascades, on the relocated line of 

 the Panama Railroad near San Pablo, near Frijoles, in the swamp southeast 

 of Diablo Ridge, and extensively near Alhajuela. This limestone is referred 

 by Doctors Dall and Vaughan to the Lower Oligocene. 



Number 7. Caimito Formation 



The Caimito formation consists of four parts, any one of which may be 

 absent. These are (a) a light gray marly argillite, which overlies the Em- 

 perador limestone ; ( b ) a yellowish and somewhat spherical weathering argil- 

 litic sandstone, which is bluish gray on fresh fracture; (c) a peculiar cal- 

 careous conglomerate with some fragments of much decayed basic rock, which 

 locally gives a bright green stain to small patches of the formation; (d) more 

 yellowish spherical weathering argillitic sandstone. "JL" is found mostly over- 

 lying the limestone and in immediate contact with it; "b" and "d" may be seen 

 in the section at Bald Hill, north of Miraflores, and "o" is thought to be the 

 rock which outcrops in the Chagres River at Barbaooas. near San Pablo. "C" 

 outcrops at Bald Hill, extensively at San Pablo, and at the site of the pro- 

 posed wireless telegraph station opposite San Pablo. This whole formation 

 has at least 400 feet of thickness. 



Number 8. Panama Formation 



The Panama formation, first named by Mill in his bulletin on the geology of 

 Panama, is a light-colored, well-bedded tuff somewhat acid in composition and 

 locally containing beds of argillite and sandy marl, it has a few fossils and 

 outcrops extensively from Miraflores to Panama and locally in some other 

 places. The formation is at least 400 feet thick and overlies the Caimito beds. 



Number 0. Gatun Formation 



This formation consists of three members: (a) About 500 feet of marls and 

 argillites containing many marine fossils and some beds of soft sandstone and 



