GEO

 The poorly sorted conglomerate and the poorly sorted graywacke contain no marine fossils and seem to be nonmarine. Marine fossils are found in thin units in the upper part of the formation, in algal limestone and in both poorly sorted and fairly well sorted subgraywacke. If the tentatively designated marine member of the Bohio(?) formation is indeed the equivalent of the lower part of the Bohio, it represents a northwestward replacement of nonmarine conglomerate by marine sandstone, siltstone, and conglomerate.
 Hill named the Bohio formation, but used the spelling Bujio (Hill, 1898, p. 183). The name was derived from Boho or Bohio Soldado, a village on the Panama Railroad located on a bluff overlooking Rio Chagres and now under the waters of Gatun Lake north of Barro Colorado Island. In Spanish orthography the name, anglicized in the Canal Zone, is Bohio. Though the little islands north of Barro Colorado Island are closer to the location of the village, the Bohio Peninsula may be considered the type region.
 In his description of outcrops Hill casually used many names that have the form of formal stratigraphic names. His expression "Bujio formation" evidently was intended to mean no more than "the formation at "Bujio." Four of his names-Bujio (Bohio) formation, Culebra clays (altered to Culebra formation), Empire limestone (altered to Emperador limestone member of Culebra formation), and Panama formation-have been preserved.
 In complete sections the Bohio formation overlies the Gatuncillo formation. So far as known the two formations are conformable, except in the Pacific coastal area, where the Bohio overlaps the Gatuncillo and rests on basement rocks. The thickness of the Bohio ranges from about 75 meters to perhaps as much as 450 meters.

 STRATIGRAPHY AND LITHOLOGY

 Gatun Lake area.-Boulder conglomerate is the most characteristic rock type of the Bohio formation in the Gatun Lake area. As shown on plate 5, the conglomerate is a rude assortment of boulders, cobbles, and pebbles. Boulders predominate and reach a diameter of 2 meters. Basalt is by far the dominant rock in the coarse constituents. In general the coarse constituents are better rounded in the northwestern part of the outcrop area, including Barro Colorado Island, where the view reproduced as plate 5 was taken. Conglomerate like that shown on plate 5 borders the launch channel between the two small islands just northwest of the first peninsula on Barro Colorado Island west of Salud Point (Orchid Island and de Lesseps Island, not labelled on plate 1). This channel is the site of the excavation


LOGY 25

 for the French locks near the village of Bohlo, mentioned in early descriptions of the Bohio formation.
 The poorly sorted coarse-grained matrix of the eonglomerate and similar graywacke forming separate beds is made up chiefly of angular grains of basalt in a clay-like binder. On Barro Colorado Island carbonaceous debris is common in medium- to coarsegrained subgraywacke containing scattered pebbles, generally poorly rounded Marine fossils were found in such sandstone in the upper part of the formation on Barro Colorado Island at locality 42g and 42i. They also were found at locality 42d in medium-grained subgraywacke that is better sorted and has little carbonaceous debris. The fossiliferous sandstone at locality 42d contains somewhat calcareous irregular lumps.
 Though conglomerate and sandstone predominate, the formation includes tuffaceous siltstone.
 The Bohio formation and Bas Obispo formation appear to intertongue. Both Hill and Howe described agglomerate (volcanic breccia of their terminology) exposed in a quarry at Bohio (Hill, 1898, p. 183; Howe, 1907, p. 112; Howe, 1908, p. 216-217), and Howe described subsurface evidence indicating equivalence of agglomerate and conglomerate (1908, p. 217-218). According to Howe, between Darien and Gamboa a few patches of conglomerate could be seen overlying agglomerate before the flooding of Gatun Lake (1908, p. 215, "in the neighborhood of Mamei, Gorgona, and Matachin"). According to Jones, in the same region conglomerate and sandstone of the Bohio formation grade into agglomerate of the Bas Obispo (1950, p. 899-900).
 MacDonald (1913, p. 568) estimated the thickness of the Bohio in the Gatun Lake area to be almost 1,000 feet (300 meters).
 Quebrancha syncline.-The Bohio formation in the Quebrancha syncline consists of a graywacke grit member and an overlying volcanic member. Both members have been described by Thompson (1944, p. 13-17). The grit member is made up of poorly sorted coarse, angular grains and scattered pebbles of basalt and thin lenses of conglomerate, in which basalt predominates. The pebbles have an observed maximum diameter of 10 centimeters. In other words, the graywacke grit closely resembles conglomerate in the Gatun Lake area, but has a much finer texture. Like the conglomerate, the grit appears to be nonmarine. Thin marine siltstone, however, was fonnd in the Basal part of the member. The maximum thickness of the member is estimated to be 450 meters.
 The volcanic member has a thickness of 30 meters. It consists, in ascending order, of porphyritic basalt (18 meters), agglomerate (9 meters), and greenish waxy