GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


bentonitic clay (3 meters). Spheroidal exfoliated masses, which weather out of the basalt and are very durable, were found by Thompson to be useful guides in mapping. This thin volcanic member evidently is a product of the eruptions that produced the Bas Obispo formation and the Las Cascades agglomerate. Study of the volcanic rocks may yield clues as to whether the volcanic member is the equivalent of part of the Bas Obispo or of part of the Las Cascadas.
 Madden basin.-The Bohio formation has been recognized only in the southeastern part of Madden basin. The outcrop area in the basin extends southeastward across the continental divide and joins the Pacific coastal area. As in the Pacific coastal area, the formation consists chiefly of poorly sorted massive conglomerate. The estimated maximum thickness is 200 meters. 'PTe absence of the Bohio in the northern part of Madden basin is attributed to overlap by the Caimito formation.
 Pacific coastal area.-In the Pacific coastal area the Bohio formation overlaps the Gatuncillo formation and lies directly on basement rocks. The Bohio thins abruptly eastward. On the west side of Rio Cabra, where the formation rests on coarse-grained diorite, the thickness is not more than 75 meters. The outcrop in the western part of the area is very wide because the grade of the slope south of the continental divide is almost the same as the dip of the formation. Cuts along the Transisthmian Highway expose massive poorly sorted conglomerate (pl. 6) and poorly sorted graywacke. Basaltic debris predominates along the highway, but the proportion of basalt decreases eastward. Thin lenses of algal limestone are interbedded with conglomerate in the upper part of the formation at localities 43-45. At locality 44 the limestone has an exposed thickness of 6o centimeters, the greatest observed thickness.

 FOSSILS AND AGE

 The bulk of the Bohio formation evidently is nonmarine, as sugested by Howe (1907, p. 112-113) and MacDonald (1915, p. 20). Silicified wood is recorded from the formation in the Bohio Pennisula (Berry, 1918, p. 32). Marine fossils, however, establish the presence of marine strata in at least the basal and upper parts of the formation.
 Smaller Foraminifera.-Sandy siltstone in the basal part of the graywacke grit tnember of the Bohio at, locality 39, in the Qetebrancia syncline, yielded the following smaller Foraminifera, identified by H. H. Renz and P. J. Bermddez:


Smaller Foraminifera from basal part of graywacke grit member of
 Bohioformation at locality 39 in Quebrancha syncline
 [Identifications by H. H. Renz and P. J. Bermddez]
 Alabamina cf. A. scitula Brady Ammospirata mexicana (Cushman) Angulogerina sp. Astacolus nuttalli (Todd and Kniker)
 sp.
 Bathysiphon eocenica Cushman and Hanna Bolivina alazanensis Cushman
 byramensis Cushman
 cf. B. gracilis Cushman and Applin
 plicatella var. mera Cushman and Ponton
 rhomboidalis (Millett)
 tectiformis Cushman
 sp.
 Bulimina alazanensis Cushman Cassidulina subglobosa Brady Chrysalogonium asperum Cushman and Stainforth
 Sp.
 Cibicides mexicanus Nuttall
 perlucidus Nuttall
 spp.
Ctavutinoides cubensis Cushman and Bermddez Cyclammina cf. C. deformis Guppy Dentalina alazanensis (Nuttall)
 cf. D. mucronata Neugeboren
 semilaevis Hantken
 Sp.
Discobis araucana (d'Orbigny) of Nuttatt Epenids umbenetua var. multisepte Koch Gaudryina (Pseudogaudryina) alazanensis Chusman Glandulina sp.
Globigerina ciperoensis Bolli
 ouachitaensis Howe and Wallace
 Sp.
Gfimbelina cubensis Palmer Guttulina byramensis (Cushman)
 sp.
Gyroidinoides cf. G. girardana (Reuss) Karreriella mexicana (Nuttall) Lagena striate (d'Orbigny) Marginslina pseudohirsuta Nuttall
 similis d'Orbigny
Nodogenerina cf. N. havanensis Cushman and Bermddez
 Sp.
Nodosaria longiscata d'Orbigny
 multilineata Bornemann
 obliqua (Lcin6)
 cf. N. pyrula d'Orbigny
 cf. N. soluta (Reuss)
 Sp.
Nonion cf. N. grateloupi (d'Orbigny)
 pompilioides (Fichtel and Moll) Osangularia mexicana (Cole) Planularia sp.
Planulina marialane Hadley
 cf. P. Weetrstorfi (Schwager)
Plectina nuttalli Cushman and Stainforth Plectofrondicularia alazanensis Cushman
 meicana (Cushman)
 vaughani Cushman


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