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bulletin: museum of comparative zoology. 





Figure 14. Guano covered Rock, 



near South End of Taboguilla 



Island. 



The accompanying sketches (Figs. 12-16) illustrate the topography 

 of the islands of Panama Bay. 



The highest of these islands are marked by three conspicuous features, 

 all of which are likewise characteristic of the mainland. The first of 



these is the rounded and pointed 

 character of the higher summits, ex- 

 actly analogous to those of the cen- 

 tral portion of the Isthmus. Upon 

 most of the islands where these high 

 summits exist, their lower profiles ex- 

 pand horizontally into distinct exten- 

 sive benches or shoulders, standing 

 about 75 feet above the water at the 

 sea line. These shoulders, together 

 with the entire summits of some of the other islands, where the high 

 pointed hills are missing, undoubtedly represent the Panama base levelled 

 plain of the mainland. 



These island benches correspond to 

 the Panama plain, and are terminated 

 abruptly by steep vertical cliffs at the 

 water's edge, corresponding in height 

 to the tidal variation of about 20 feet. 

 These cliffs are often concave in pro- 

 file, and it is apparent upon every side 

 that they are produced by the intense 



wave erosion which is at present rapidly undermining them. Fre- 

 quently the beating of the waves has cut a narrow passage through 



some projecting cape, completely sev- 

 ering small islets from the larger 

 body with which it was but recently 

 connected. Every stage in this pro- 

 cess can be seen in various places. 

 It seems to me that : — 



1. All of the islands of Panama 

 Bay are composed in part of the an- 

 cient looking, black igneous rock, 

 apparently of the same character as those found upon the Isthmus, 

 interassociated with the Panama formation, which can be seen upon 

 the island of Naos outcropping close to the water, as at the city of 

 Panama. 



Figure 15. San Jose Rock, Panama 



Bay, Remnant of Panama 



Base Level. 



Figure 16. Basaltic Rock, South 

 End of Taboguilla Island. 



