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 Бес- 
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 4 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 4 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 4 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 
