HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 197 
To describe this configuration as a slope to the Pacific would convey an 
erroneous impression to the reader, for it is not a coastal slope at all in 
the ordinary sense of this term, but a rugged hilly 
country like the central region, which extends straight, 
not only to the water's edge, but far out across the 
waters of Panama Bay to the south edge of the con- 
tinental outline off Morato and Burico Points. Flat 
swamp-like indentations have been made into this hilly 
country, by ancient erosion and subsidence. By sedi- 
mentation these indentations have been filled with 
littoral deposits which in turn have again been ele- 
vated into low swamp lands, representing ancient em- 
bayments or niches in the otherwise rugged coast, the 
chief of which is Panama Bay, surrounded on three 
sides by the rough hilly country, and in which stand 
a few islets of volcanic rock. 
Thus it will be seen that, as on the Caribbean side, 
there is no such feature as a coastal plain uniformly 
skirting the coast for great distances, but that the 
rugged topography, except where indented by the Rio 
Grande swamp level, abruptly terminates at tho oce- 
anic waters, ама even continues out into the waters of 
Panama Bay many miles from the shore (Fig. 10), as 
seen in the islands of Naos, Tobago, Perico, Flamenco, 
San José, and Changargi,). also see Figs. 12, 13, 14, 15, 
16, pages 203, 204,) whose summits and outlines, pro- 
jecting above the water, are almost in every detail a 
repetition of the long eroded geography and geology of 
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the mainland with which they undoubtedly were at one 
time continuous. (See Plate XVIIL) Between the 
level of the Rio Grande swamp and the rough sum- 
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mit topography of both the mainland and the islands, | 
however, an indistinot but persistent bench could be il i» 
| 
discerned, representing an ancient base levelled plain, 
which will be described as the Panama base level. 
Looking from the Caribbean side through the Cule- 
bra Pass, some low rounded hills of igneous rock can 
They apparently constitute a continuation on the Pacific side 
be seen. 
of the Culebra and Lirio igneous masses. In this hill of igneous rock 
near Paraiso the actual summit cut of the railroad is located. (See 
VOL. XXVIII. — NO. 5, 4 
