known thickness for limestone of Emperador type. A view of this limestone is shown in plate 9. It was
-recently identified as the Emperador limestone member of the Culebra formation (Woodring and Thompson, 1949, p. 237), but is now thought to represent the La Boca member. It is in an area where the La Boca is known to be present, although no continuity with other La Boca rocks has been established. If the limestone is now correctly identified, the La Boca member overlaps onto the Bas Obispo formation. The strata in Gaillard Cut between canal stations 1720 and 1730, described by MacDonald as "light-colored tuff bed locally overlapping Culebra beds" may possibly represent overlapping La Boca (Natl. Acad. Sci., 1924, p. 52, fIg. 4). Limestone of the La Boca near Red Tank (locality 131) was referred by MacDonald to the Emperador member of the Culebra formation, and sandstone and agglomerate overlying the limestone to the Caimito formation (MacDonald, 1919, p. 534, "section at Bald Hill near Miraflores Locks"; for other locality data see p. 124). In fact, MacDonald used the section near Red Tank to define the Caimito formation and its stratigraphic relations to the Emperador limestone member of the Culebra formation (MacDonald, 1913, p. 569).
 The Pedro Miguel agglomerate member is a lens of essentially coarse-grained pyroclastic rocks. In the Pedro Miguel area, the type region, these rocks overlie the Cucaracha formation. The lower part of the pyroclastic rocks, like the lower part of the La Boca marine member, apparently is the equivalent of the upper part of thick Cucaracha sections. Farther south the pyroclastics appear as a tongue in the lower part of the La Boca marine member. The pyroclastic rocks of the Pedro Miguel member, as described by Thompson (1947a, p. 18-19), consist chiefly of fine- to very coarse-grained agglomerate. Bedding and sorting are poor to moderately well developed. Fine-grained tuff is interbedded with the agglomerate. The thickness of the Pedro Miguel member is variable, but the maximum averages about 100 meters. Agglomerate of the Pedro Miguel in the Miraflores area was formerly considered part of the Las Cascadas agglomerate or was doubtfully referred to that formation (MacDonald, 1919, p. 533). Howe, however, realized that agglomerate near the continental divide rests on the Culebra formation (1908, p. 222-223). (The Cucaracha formation had not yet been differentiated.) Like MacDonald, he thought that agglomerate farther south near Corozal is of pre-Culebra age (Howe, 1908, p. 223).
 Much agglomerate is known to be present in an unmapped area between Madden Highway and Curundu. It is not known, however, whether all this agglomerate represents the Pedro Miguel member, as shown on


plate 1, or what rocks other than aglomerate crop out in the area.
 The Panama formation proper is made up of tuff, tuffaceous siltstone, tuffaceous sandstone, and agglomerate. They evidently represent nonmarine essentially fine-grained tuff and tuffaceous strata that interfinger with and overlie the La Boca marine member and the Pedro Miguel agglomerate member. The geologic map (pl. 1) suggests that in the Pacific coastal area the Panama formation proper overlaps part of the Caimito formation, but that relation needs confirmation. Tuff characteristic of the Panamtd formation is light gray, rhyolitic, and contains much pumnice and minute fragments of glass (Hill, 1898, p. 200-201; Howe, 1907, p. 116-117). Such tuff is exposed along the water front in Panamd and in street cuts in Diablo Heights. Similar tuff near Miraflores, now included in the La Boca marine member, was informally designated the Miraflores pumice by Hill (1898, p. 198-199), a name he suppressed on a later page (Hill, 1898, p. 206). Comparison of the volcanic constituents of the Panamd amtd Caimito formations may afford a basis for confirmintg or rejecting earlier correlations of tuff in the Panami formation with rhyolitic tuff along the canal north of the continental divide (Hill, 1898, p. 201; Bertrand and Zfrcher, 1899, p. 91; Howe, 1907, p. 117). The apparent overlap of the La Boca marine member of the Panamii formation across the Cucaracha and Culebra formations indicates that their correlation deserves further consideration. In the ineantime, however, it is not accepted.
 FOSSILS AND AGE
 The only available fossils were found in the La Boca marine member.
 Smaller Foraminifera.-Smaller Foraminifera are fairly abundant in fine-grained strata. They represent a more open-sea marine environment than the meager fauna of the Culebra formation. M. N. Bramlette, who examined the outcrop sample from locality 124 and some subsurface samples, points out the abundance of Siphogenerina transversa. The type locality of that species (Geological Survey locality 6010, 130 of present report) is in strata of the La Boca member penetrated in the canal excavation between Paraiso and Pedro Miguel. Siphogenerina also is found in calcareous sandstone at locality 128. Both the type locality of Siphogenerina transverse and Geological Survey locality 6009 were assigned to the Culebra formation in Cushmaim's account of Canal Zone smaller Foraminifera (Cushman, 1918).
 Larger Foraminifera.-The type locality of Lepidocyclina miraflorensis (locality 132a), a lepidocycline species, represents the La Boca marine member. It has been suggested that that locality is near the rail-


GEOLOGY


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