178 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
shells. This marl is not entirely calcareous, however, but is partly 
composed of volcanic débris. It has been studied by Mr. H. W. Turner 
of the U. S. Geological Survey, who reports upon it as follows : — 
“ Foraminifera make up the greater part of the section examined. Іп 
addition there are fragments of a slightly greenish augite, and a deep 
brownish green strongly pleochroic hornblende. A few prisms of feldspar, 
and very abundant minute clear grains with low gray interference colors 
presumably also feldspar. The hornblende is brownish (the A ray brown 
and the C ray deep greenish brown). ‘The augite, hornblende, and feld- 
spar probably all came from volcanic rocks.” 
At this locality it was impossible to ascertain the stratigraphic rela- 
tion of this foraminiferal material to the Bujio bluff of igneous material, 
but from their relative positions it apparently lies unconformably 
against the latter. Three fourths of a mile below Bujio in the cutting 
of the canal the same rock crops out, much jointed and so broken that 
its beds dip as high as 20 per cent in places. This is a more recent 
and less decomposed exposure of the same foraminiferal beds than at 
the house of the Chef de Section. One mile below, northwest of Bujio, 
we reached the Chagres, and in the lower part of its banks, composed 
of red clay, the foraminiferal marls can again be seen at the water’s 
edge in their unweathered condition. 
Crossing the Chagres we came to the plantation of Mr. Shaffer of 
the Panama Railway Company, who procured canoes to take me down 
Figure 3. Section on Mr. Shaffer's Farm near Pena Negra, showing Contact 
of Foraminiferal Marl with Boulder Formation, 
25 kilometers of the completed canal between this point and Colon. 
About 200 yards up the river from Mr. Shaffer’s house is a hill known 
as the Pena Negra. This is of the same type of topography as nearly 
all the hills of the Isthmus, sharply pointed, with precipitous slopes, 
covered with dense vegetation, and is apparently in strike with the hills 
