GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


pally of lime-cemented coquina made up of small fragments of barnacles, shells, echinoid spines, and corals (pls. 11, 12). Barnacle fragments predominate at many localities and cross-bedding is common. Lenses of medium- to coarse-grained sandstone occur in the coquina. Descriptions of outcrops of the Toro have been published by MacDonald (1919, p. 544-545) and Olsson (1942, p. 246).
 The Chagres sandstone proper is made up of massive generally fine-grained sandstone and some siltstone (pl. 13). Unlike the Gatun formation, the Chagres is not known to include conglomerate or tuff, and the sandstone itself contains less volcanic material than sandstone of the Gatun.
 FOSSILS AND AGE
 Mollusks.-A few molds of mollusks from Olsson's Anomia zone are included in the families covered by chapter A of the present report: Calliostoma? sp. and Turritella gatunensis? from locality 194; Turritella altilira s. 1. from locality 195; Turbo aff. T. castaneus, Turritella gatunensis?, and Turritella mimetes? from locality 195. Olsson's Anomia zone (Olsson, 1942, p. 246-247) appears to be part of the shallow-water calcareous deposits forming the overlapping Toro limestone member of the Chagres sandstone rather than part of the Gatun formation.
 A new species of Calliostoma, C. metalium (localities 206, 206a), an unidentified mold of Crucibulum (locality 201), and Stigmaulax guppiana (locality 208) occur in the Chagres sandstone proper. The mollusks of the Chagres sandstone proper, unlike those of the Toro limestone member, indicate deposition in water of moderate depth.
 Echinoid.-A large species of Clypeaster, found in the Toro limestone member at locality 196 (Olsson's Anomia zone), is identified by C. W. Cooke as C. aff. C. bowersi. C. bowersi occurs in the Imperial formation of the Colorado Desert, of disputed Miocene or Pliocene age (probably late Miocene).
 Age.-The Chagres sandstone is close to the border between Miocene and Pliocene; it has been assigned to both series. Preliminary examination of the mollusks suggests early Pliocene, despite the presence of a few Gatun species, such as Stigmaulax guppiana, and of other species that have Gatun affinities.
 PLEISTOCENE SERIES
 STRATIGRAPHY AND LITHOLOGY
 Pleistocene marine deposits occur at altitudes of a few feet above sea level and in the seaward part of buried valleys are interbedded with swamp and stream deposits. Swamp and stream deposits filling buried valleys extend as far inland as Gamboa on the Caribbean side of the Canal Zone and as far as Miraflores Locks on


the Pacific side (Thompson, 1947a, p. 22). Black organic muck is the most widely distributed type of deposit. In fact, the geologists of the Geological Section of the Special Engineering Division used the in- a formal designations Atlantic muck and Pacific muck for the Pleistocene deposits (Thompson, 1947a, p. 22). According to Thompson's description, much of the black muck represents swamp deposits and is a mixture of silt, very fine-grained organic debris, and partly carbonized wood, stems, and leaves. Layers of marine fossils are found in black organic silt and calcareous mud containing plant matter. They were encountered at the north end of the excavation for the Gatun Locks and in ditches in swamps north and east of Mount Hope (Brown and Pilsbry, 1913, p. 493-494; MacDonald, 1919, p. 544). Brown and Pilsbry casually used the name Mount Hope formation, which they attributed to W. B. Scott, for Pleistocene strata near Mount Hope (Brown and Pilsbry, 1913a, p. 493).
 FOSSILS AND AGE
 Corals.-Corals in collections from localities near Mt. Hope have been listed by Brown and Pilsbry (1913a, p. 497) and Vaughan (1919b, p. 563). They evidently represent reef-flat species.
 Mollusks.-A few new species of mollusks were described by Dall (1912, p. 1-6) and Brown and Pilsbry (1913a). Brown and Pilsbry listed the species in the two collections they studied. The few species in their collection from the north end of the Gatun Locks excavation indicate brackish water and the deposits themselves point to deposition in a swamp. The depositional environment of the large number of marine species in their collection from a locality near Mount Hope, and in MacDonald's collections from the same region, is uncertain on the basis of published data.
 Contrary to Dall's statement (1912, p. 1), MacDonald's collections from the Caribbean side do not contain any species now living along the Pacific side.
 The Pleistocene mollusks are not described in the systematic part of the present report.
 Age.-With the exception of the new species of mollusks, the identified fossils from the Pleistocene marine deposits on the Caribbean side of the Canal Zone are known to be living in the Caribbean Sea. Dall, and Brown and Pilsbry realized that their new species may be found to be living when the fauna along the Caribbean coast of Panama is better known. The Pleistocene deposits-at least the marine deposits-probably are of late Pleistocene age, but may be too old for radiocarbon dating.
CORRELATION OF TERTIARY FORMATIONS IN DIFFERENT AREAS
 Correlation of the Tertiary formations in different areas and age assignments, as adopted in the present


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