E. Howe — Geology of the Isthmus of Panama. 225 



Nearer Las Cascadas bowlder-like concretionary masses of 

 hard crystalline limestone, one to four feet in length, are pre- 

 served in red clays of decomposition near the railway and 

 canal. Fragments of a Pecten and a tube-like Xylotrya were 

 collected from one of these limestones but their age could not 

 be determined. 



Age of the Culebra beds. — Hill made a careful study of the 

 Culebra beds, hut only succeeded in finding fossils in the 

 Empire limestone, mostly foraminifera that Bagg considered 

 representative of the Eocene, and as quoted in Hill's report, 

 he correlated this limestone with the Peiia Blanca marl.* In 

 material that I collected in the vicinity of Las Cascadas from 

 rocks that I believed to belong to the same calcareous horizons 

 as the Empire limestone, Dr. Dall failed to find any species 

 from which the age of these beds could be determined. Ber- 

 trand and Ziircher, however, collected from the same localities 

 and their material was determined by Douville as representing 

 the Burdigalian Miocene, or the equivalent of the beds exposed 

 at Kilometer 10 near Gatun. f The French geologists regarded 

 the Empire limestone as belonging to the upper part of the 

 Culebra beds and equivalent to the Vamos Yamos beds of the 

 Caribbean slope. In the vicinity of Pedro Miguel Bertrand 

 and Ziircher found fossils that were correlated with those from 

 Las Cascadas. Fossils from my collection at the same locality 

 were determined by Dr. Dall as probably representing an 

 Oligocene reef deposit, while beneath them a typical Claiborne 

 fauna was found in a compact impure limestone. 



It is probable that the Claiborne horizon at Pedro Miguel is 

 the one that Bertrand and Ziircher correlate with the beds at 

 Las Cascadas, since the fauna of both is regarded by them as 

 identical with that preserved at Kilometer 10 near Gatun. It 

 is in collections from the Gatun locality made by Hill and 

 myself that Dall finds his most typical Claiborne fossils. At 

 both Pedro Miguel and Las Cascadas the position of the f os- 

 siferous beds appears to be at or very near the top of the 

 Culebra section, and in the absence of determinable fossils from 

 lower horizons it seems reasonable to refer the Culebra beds as 

 a whole to the same period as that in which the Bohio forma- 

 tion was deposited. The abundance of carbonaceous shales, 

 seams of lignite and plant remains, together with fragments of 

 a melanian found in the canal cut near Culebra, suggest that 

 most of the beds below the limestone horizons were deposited 

 in fresh water. 



Limestones of the Upper Chagres. — Following the Chagres 

 headward in a northeasterly direction from Matachin, where 

 the river, turns sharply to the northwest and flows toward the 



* Op. cit., p. 272, 275. f Op. cit., pp. 6-9. 



