Soon after American operations were started, Ernest Howe was employed by the Isthmian Canal Commission to study the geology. Though he was in the Canal Zone only five months during 1906 and 1907, his reports clearly set forth the essential features and went a long way toward systematizing the stratigraphic nomenclature (Howe, 1907, 1907a, 1908). Appointment of D. F. MacDonald, formerly of the U. S. Geological Survey, as resident geologist during the last two years of the construction period (1911-13) led to further advances and to the gathering of much information (MacDonald, 1913, 1913a, 1915, 1919). Only the first of the four publications by MacDonald just cited is generally cited on the following pages in the discussion of the stratigraphy. The others contain practically identical descriptions, aside from new names. Many of the fossils described in the present report were collected by MacDonald or by MacDonald and Vaughan, when Vaughan collaborated with him in the latter part of 1911. The stratigraphy, as worked out by MacDonald and Vaughan, was described in Bulletin 103 of the U. S. National Museum (Vaughan, 1919). Though Bulletin 103 was issued in 1919, many of its parts were published separately in 1918, and Jackson's part on the echinoids was issued separately in 1917 and again in 1918. In the preparation of Bulletin 103 Vaughan enlisted the services of a group of paleontologists, who described practically all the Canal Zone fossils then available in the National Museum collections, except the mollusks. Not all the fossils described in Bulletin 103 are mentioned in the summaries on the following pages. Calcareous algae (M. A. Howe, 1918), land plants (Berry, 1918), Bryozoa (Canu and Bassler, 1918), decapod crustaceans (Rathbun, 1918), and ,barnacles (Pilsbry, 1918) are omitted.
 The third period of marked advances resulted from investigations, including the study of some 2,000 cores, of the Geological Section of the Special Engineering Division of the Panama Canal, carried out under the direction of T. F. Thompson. The surface and subsurface studies undertaken by this staff of geologists were for the most part directly related to the Third Locks and Sea-level Conversion Route projects. The published reports prepared by the Geological Section include summaries of the geology and more detailed descriptions of particular areas (Thompson, 1943, 1943a, 1944, 1947, 1947a). The oldest rocks, older than any along the canal, were found to consist of a basement of unknown age overlain by deposits of Eocene age. Agglomerate along the southeastern part of the canal, formerly correlated with agglomerate underlying the Culebra formation, overlies the Culebra. Marine deposits in the same region formerly identified


as the Culebra formation, also are younger than that formation.
 PURPOSE AND SCOPE OF REPORT
 The National Museum's collection of fossil mollusks from the Canal Zone represent a collecting span of a century. Not many collections, however, were received prior to 1911, when the fossils collected by MacDonald began to arrive. It was expected that the mollusks would be studied by W. H. Dall, the dean of American Tertiary invertebrate paleontologists. For the most part he got no further than generic identification of MacDonald's early collections. Therefore the mollusks-the most abundant fossils then availablewere omitted when Bulletin 103 was assembled. A considerable number of mollusks from the richly fossiliferous Gatun formation, collected while the canal was being constructed, were described by Toula (1909, 1911) and by Brown and Pilsbry (1911, 1913) before the publication of Bulletin 103. Other Gatun species have been recorded in scattered publications, and also a few from other formations (Culebra formation and its Emperador limestone member, Toro limestone member of Chagres sandstone). Nevertheless the National Museum collections represent much valuable information, which is not in useable form until the fossils are adequately studied. The present report is designed to meet that need.
 The collections obtained before and during construction of the canal are especially valuable, for very few of them can be duplicated. Some of them, particularly in Gaillard Cut, represent excavated prisms of rock; many other localities are now submerged; still others are inaccessible through the rapid disintegration of rock and the rapid growth of a thick cover of vegetation.
 To take advantage of the store of information gathered by the Geological Section of the Special Engineering Division, field work in the Canal Zone was undertaken during the dry season early in 1947. By that time it was evident that work in the fairly complete succession of lower and middle Tertiary marine formations in Panami east of the Canal Zone was needed to interpret the less complete partly marine succession of the same age in the Zone. Further field work was carried out early in 1949 and early in 1954. The work in 1954 was limited to Barro Colorado Island and nearby parts of the Gatun Lake area. The geology of Barro Colorado is to be described in a separate publication.
 The field work was designed as a stratigraphic and paleontologic project-not as a mapping project, which would have been very time-consuming. Some kind of map, however, was needed to show the localities


INTRODUCTION


3