HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 



197 



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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 Eurico 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 the oce- 

 anic waters, and 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 Jose, and Changargi,) also see Figs. 12, 13, 14, 15, 

 16, pages 203, 201,) whose summits and outlines, pro- 

 jecting above the water, are almost in every detail a 

 repetition of the long eroded geography and geology of 

 the mainland with which they undoubtedly were at one 

 time continuous. (See Plate XVIII.) Between the 

 level of the Rio Grande swamp and the rough sum- 

 mit topography of both the mainland and the islands, 

 however, an indistinct but persistent bench could be 

 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 

 be seen. They apparently constitute a continuation on the Pacific side 

 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 





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