VI PREFACE. 



data are not sufficient. It is probable that three and perhaps four 

 horizons will be discriminated within the Gatun formation. Other 

 groups of organisms are adequate for correlation purposes in most 

 or all of the other geologic formations, but for the Gatun formation 

 the principal reliance must be placed on the mollusks. The collec- 

 tions of mollusks made by Doctor MacDonald and myself is very 

 extensive, and the greatest possible care was taken in obtaining full 

 information on the stratigraphic relations of the material. It is 

 hoped that a report commensurate with the size and importance of 

 the collection may not be much longer delayed. 



The series of papers here presented comprises all of the pale- 

 ontologic memoirs that have been completed. These are immedi- 

 ately followed by descriptions of the geologic exposures where 

 collections of fossils were made, with summaries of the fossils ac- 

 cording to their stratigraphic occurrence, and a chapter on the 

 geologic correlation of the fossiliferous formations, both with other 

 American and with European formations. It is intended that Doctor 

 MacDonald's comprehensive general report will be published soon 

 after this series of memoirs has been issued. 



The names of the geologic formations used in the paleontologic 

 reports are the same as those employed by Doctor MacDonald in 

 Bulletin 86 of the United States Bureau of Mines, to which reference 

 is made on page v of this preface. 



I wish to thank the officials of the Canal Commission, particularly 

 Maj. Gen. Goethals, Director George Otis Smith, and Chief Geologist. 

 David White of the United States Geological Survey, and Dr. Charles 

 D. Walcott, Secretary of the Smithsonian Institution, for the sup- 

 port they have given these investigations. To my colleagues out- 

 side the Geological Survey and United States National Museum, 

 Dr. Marshall A. Howe, Prof. E. W. Berry, Dr. Robert T. Jackson, 

 Mr. F. Canu, and Prof. H. A. Pilsbry, who has collaborated in this 

 work, I am under deep obligations; and it is a pleasure to record my 

 appreciation of the efforts of my official colleagues, Dr. D. F. Mao 

 Donald, Dr. Joseph A. Cushman, Dr. C.Wythe Cooke, Dr. R. S. Bassler, 

 Dr. Mary J. Rathbun, and Mr. J. W. Gidley, all of whom have labored 

 harmoniously to bring a large undertaking to a successful conclusion. 



Thomas Wayland Vaughan. 

 September 15, 1919. 



