HILL : GEOLOGY OF THE ISTHMUS OF PANAMA. 181 



Vamos beds, as shown by Dr. Ball's report upon the fossils. About 

 half a mile south of Gatun on the canal is seen a bluff composed en- 

 tirely of green marls, and containing many large and beautiful fossils. 

 Otherwise than a few little joints and faults, it has almost a horizon- 

 tal structure, dipping slightly coastward. 



Kilometer 9. — The greensand marls continue at the low water line of 

 the river, the upper banks being red clay. 



Kilometer 8. — From here on to Colon the canal is mostly cut through 

 the swamps, only one more outcrop of the older hill structure being 

 exposed. 



Kilometer 6. — The canal here cuts the eastern base of the Mindi 

 Hills, exposing a bluff over 100 feet in height, which is composed entirely 

 of the Tertiary greensand marls previously noted since leaving Gatun. 

 Topographically the Mindi Hills are evidently a continuation of the 

 Monkey Hill base level, but the strata composing them are older, be- 

 longing to the Eocene, while the latter are of the Oligocene age, as shown 

 by Dall. 



From Kilometer 5 to Kilometer 3. — After passing the cut through 

 Mindi Hill the canal continues through the swamps. The terreplanes 

 thrown up by the dredges are all the fossiliferous sandy material dredged 

 up from the canal, the bottom of the canal extending to 28 feet below sea 

 level, and is the same as the material of the coastal swamps described 

 on page 173, and contains innumerable shells of species not older than 

 the Pleistocene, many of which are still living in the adjacent water. 



Kilometer 4£. — Here the canal touches the land, or inner end, of Nava 

 Bay. We stopped to study the swamp formation which here forms the 

 interior border of the bay, and ascertained that it is made up of the same 

 material previously described along the canal and abounding in the same 

 mollusca. The destructive effect of the choppy surf is rapidly destroy- 

 ing the coast at this point. 



From kilometer 4£ to the terminus at Colon the canal continues 

 through the swamp formation. 



Fox River and Manzanilla Bay. — In order to examine further the 

 formations of the coast I passed through Fox River and into the rear end 

 of Manzanilla Bay, and thence up the artificial cut known as the devia- 

 tion, entering the back end of the bay. The swamp lands surround- 

 ing the outlet of the deviation for about half a kilometer of its distance 

 are composed of the same recent fossiliferous formation as the Mindi 

 swamp and contained similar littoral shells. Inland the deviation passes 

 a vertical cutting of over 50 feet, through the base of the Monkey Hills. 



VOL. XXVIII. — no. 5. 3 



