336 PROCEEDINGS OF THE ACADEMY OF [April, 



FAUNA OF THE GATUN FORMATION, ISTHMUS OF PANAMA- 

 BY AMOS P. BROWN AND HENRY A. PILSBRY. 



The collection of fossils studied in this paper was made by one of us 

 (Brown) during two visits to the Isthmus in April and in August, 1910. 

 With the exception of a tooth of a shark 1 and a few specimens of 

 Oliva from Monkey Hill all come from the excavations for the locks 

 at Gatun. The Oliva taken at Monkey Hill is the same species found 

 plentifully at the Gatun excavation. The specimens were collected 

 from dumps and fills along the railway as well as from the dumps in 

 the vicinity of Gatun. 



A rapid reconnaissance of the stratigraphy along the line of the railway 

 from Colon to Empire and along the canal from Colon to Gatun seemed 

 to indicate that the formations, from the highest exposures at Monkey 

 Hill (Mount Hope) to the lowest that contain molluscan remains at 

 Bohio, form one stratigraphic unit, the base of which is to be found 

 at Bohio and the top at Monkey Hill. This was the impression formed 

 by a study of the stratigraphy on the ground. As shown below, the 

 study of the fossils collected, and a survey of the literature on the 

 Isthmian formations, bears out his impression formed in the field. 

 The thickness of this Gatun formation is probably not much above 

 400 feet, judging from exposures and borings at Gatun. It is dredged 

 from the canal at more than four miles north of Gatun, being here 

 encountered at 18 feet below water level. 



If this is correct that the mollusk-bearing formations from Bohio 

 to the sea at Colon form one stratigraphic unit (and they appear to be 

 one f aunal unit) , the Gatun Formation will include beds that have been 

 variously called Bohio, Gatun, Monkey Hill, Culebra and Vamos- 

 Vamos. 



The recognition of Eocene in the Isthmian section rests upon fossils 

 from the "Vamos a Vamos or Gatun beds" collected by Robert T. 

 Hill and examined by Dr. Win. H. Dall. These fossils occur as 

 " pseudomorphs in calcite in a tough matrix, and difficult to extract 

 in good condition." The following Eocene (Claiborne) species were 

 " noted on a rapid examination" 2 by Dr. Dall: 



1 Carcharias megalodon Ag. 



2 Bull. Mus. Camp. Zool., vol. 28, p. 273. The genera noted without specific 

 identifications are such as are found in the Oligocene beds. 



