GEOLOGY AND PALEONTOLOGY OF CANAL ZONE


 T. bifastigata was found only in the lower part of the Gatun formation. Though it has no living allies in the Caribbean Sea, it is closely related to T. broderipiana d'Orbigny, a living Panamic species that lacks sutural collars or has greatly subdued collars. The early intermediate whorls of T. broderipiana are like those of T. bifastigata, but the middle spiral and the spiral adjoining the anterior suture are stronger, and the spiral midway between them is weaker. The early whorls of T. broderipiana enlarge rapidly. A middle spiral asd one on both sides of it appear on the first sculptured whorl, and an anterior sutural spiral on the next whorl. With further growth the middle and anterior sutural spirals increase in strength, the others diminish. The middle spiral strongly carinates the early whorls, except the first. The first three whorls bear slightly arcuate exaggerated growth lines above the carina.
 T. bifastigata and T. seimetes represent Merriam's T. broderipiana stock (Merriam, 1941, pp. 50-51).
 Occurrence: Lower part of Gatun formation (middle Miocene), localities 137, 137a. Upper part of Zorritos formation (late early Miocene), Perd. LOCALITIES AT WHICH FOSSILS WERE COLLECTED

 The localities at which fossils were collected are described in the following list and the numbers used for them in the present report are correlated with the permanent numbers recorded in the Geological Survey's Cenozoic invertebrate register. The list includes not only localities that yielded fossil mollusks, but also some important localities where only other kinds of fossils were collected. Unless otherwise specified, the report locality numbers are plotted on the general geologic map (pl. 1). As noted in the list, localities in the Gaillard Cut area are plotted on the large-scale geologic map of that area (pl. 2). Some early collections have such inadequate data that they cannot be plotted, and other localities are not plotted to avoid congestion of the map. Early localities that are now submerged are shown on plate 1 and plate 2 by a special symbol, even though the plotted location may be only approximate. Some submerged localities, however, cannot be plotted even approximately.
 Before the construction of the canal, Rio Chagres flowed southwestward to the present site of Gamboa and there turned northwestward to the Caribbean Sea. It was first dammed near Gatun to form Gatun Lake and later was dammed upstream from Gamboa to form Madden Lake. The course of the river and the location of the Panama Railroad before the canal was built are shown on the map accompanying the publication cited under Bertrand and Ztircher (1899).


The relocated line of the Panama Railroad, cited in the following list, is the present line constructed in 1911-13.


No. USGs
"sed sin Cenozoic Field "hs No. N. report


8400























17433




17432


131








131a 132
















150 118 114 115


 Description of locality



 GATUNCILLO FORMATION

Madden basin, Panamd. South side
 of Rio Pequeni near head of Madden Lake, 120 meters west of former Canal Zone Pequeni Police Sub-. station. Thin-bedded limestone, 2.5 meters above base of Gatuncillo formation. T. F. Thompson and W. P. Woodring, 1949. Larger Foraminifera (Cole, 1952 [1953]). Same locality. Thin-bedded nodularweathering limestone, 5.5 to 7 meters higher stratigraphieally. T. F. Thompson and W. F. Woodring, 1949. Larger Foraminifera (Cole,
 1952 [1953]). Not plotted.
Madden basin, Panamd. West shore of
 Madden Lake at abandoned Salamanca Gaging station. Fairly soft limestone. T. F. Thompson and W. P. Woodring, 1949. Larger Foraminifera (Cole, 1952 [1953]). Madden basin, Panamd. San Juan de Pequenf, on Rio Pequeni about 1 kilometer upstream from junction with Rio Clsagres. Fragmental limestone. E. N. Lloyd, 1919. Now submerged. Topotypes of Lepidocyclina chaperi and other larger Foraminifera (Vaughan, 1926). For location of San Juan de Pequenl see Reeves and Ross, 1930, p1. 5. Madden basis, FanamA. Trail west of Madden Lake, 4.8 kilometers north of Madden Dam. Limestone. T. F. Thompson and W. P. Woodring, 1949. Larger Foraminifera (Cole, 1952 [1953]).
Madden basin, Panamd. Trail north of Rio Puente, 2 kilometers northeast of Natural Bridge (Puente Natural). Thin-bedded limestone. T. F. Thompson and W. P. Woodring, 1949. Larger Foraminifera. Madden basin, Panaml. Lumber road north of Rio Puente, 1.7 kilometers east-southeast of Natural Bridge. Limestone. T. F. Thompson and W. P. Woodring, 1949.
Madden basin, Panamd. Lumber road north of Rio Puente, 1.6 kilometers east-southeast of Natural Bridge. Limestone. T. F. Thompson and W. P. Woodring, 1949.


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