HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 179 



of igneous material at Bujio. The Chagres has cut a precipitous bluff 

 into the side of this hill, creating a fresh exposure where the relation of 

 the rocks may be studied. This hill is composed of a mass of the 

 peculiar rounded igneous rocks which elsewhere are described more fully. 

 This material continues from the summit of the hill to the water's edge. 

 On the Caribbean side of this hill is a clean contact of the marine 

 sedimentary rocks, resting unconformably upon and against this old 

 transported volcanic material. The basement Tertiary rocks are the 

 same foraminiferal marls traced from the mamelon of the Chef de Sec- 

 tion at Bujio, and interstratified with it boulders of the igneous rocks 

 derived from the adjacent beds. This contact, as well as the igneous 

 material contained in the sedimentaries, clearly proves the important 

 point that some of the Tertiary sediments are of later age, and de- 

 posited against some of the old igneous material. The character of 

 this contact is given in Figure 3. From their geographic position and 

 inclination I was inclined to believe that these foraminiferal marls were 

 the lowest of the fossiliferous Tertiary sediments of this locality. Dr. 

 Dall, however, is inclined from paleontologic testimony to believe that 

 they belong above the Vamos a Vamos beds next to be described. If his 

 conclusion is correct, the present relation of the disturbed beds would 

 only be explained by a complete overthrow, which I do not think 

 probable. 



Section along Line of Panama Canal. — From Pena Negra we 

 paddled down the Chagres and Panama Canal, 22 kilometers, to Colon, 

 securing under better conditions of observation another and parallel 

 section of the country traversed by rail from Colon to Bujio. 



Kilometer 22 to Kilometer 20. — Our boat follows the Chagres, touch- 

 ing the shores frequently to examine the nature of the banks. The 

 dark green and black marls of the Tertiary are the only rocks met with 

 along the river. From such glimpses of the substructure as could be 

 obtained beneath the red alluvium of the river, it could be seen that 

 these Tertiary sediments had been much disturbed and distorted since 

 their deposition. 



Kilometer 20. — The Vamos a Vamos Beds. — We have abandoned 

 the old river channel, and are now in the main canal cutting. On the 

 left hand side of the river at Vamos a Vamos rises a vertical bluff some 

 200 feet in height, which is apparently an outlying hill of the Quebran- 

 cho range previously described. The rock composing this bluff is so 

 black in color (greenish black on fracture) that at first glance it seemed 

 to be composed of igneous material as Professor Wolff's report has shown 



