GEOLOGY


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ase from Panam6 sheet of American Geographical Society's map of Hispanic America



 Scale 1:1,000,000
 5 0

 10 0


 EXPLANATION




 0 8 ] h T(, <I k 1 zc/2//2 Chagres sandstone 0 ( Caimito(?) formation





 Gatun formation 0 Undifferentiated volcanic and intrusive rocks


 Contact
 180
 Locality where fossils were collected Figure 3.-Reconnaissance geologic map of Caribbean coastal part of Panamad irnmediatelywest of Canal!Zone.
 Base from Panam0 sheet of American Geographical Society's map of Hispanic America.


interpretation, however, and the areal geology shown on figure 3 need confirmation. The matrix of the fossils consists of silty very fine-grained sandstone and sandy siltstone.
 FOSSILS AND AGE

 Sonaller Foraminifera.-Smaller Foraminifera from the Gatun formation were recorded by Cushman (1918). Marly siltstone in the upper part of the formation in the Canal Zone contains more species than those of Cushman's report.


 Molluosk.-Mollusks are by far the most abundant and widespread fossils in the Gatun formation. The collections at the U. S. National Museum represent a collecting span of a century. In 1853 Blake collected three species described two years later by Conrad (1855, p. 18; 1857, p. 328, pl. 6, figs. 53-55). Only one of the fossils found by Blake is known to have survived: the type of "Gratelupia?" mactropsis [Lirophora mactropsis], a double-valve mold to which some inner shell material clings. Blake's form of locality citation is equivocal:


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31*00'


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25 Miles

 50 KilometerE