hill: geology of THE ISTHMUS OF PANAMA. 249 



sands seen in the hills in the edge of Limon rise to a height of over 

 fifty feet above the sea, and contain casts of marine shells. The Pleisto- 

 cene of the Isthmus proper is fully detailed elsewhere in this report. 



It is an important fact, however, that reef making corals were found 

 by both Gabb and the writer in the " Pliocene " of Port Limon beneath 

 the later sand formations. If the fringing coral reefs of Colon and Limon 

 are Pleistocene in origin, then the time of reef building extends through 

 at least two epochs, for the fringing reefs are also of later origin than 

 those of the alleged Pliocene formation above mentioned. 



The non-marine aggradatioual deposits of the large river valleys of the 

 region, which seem to grade coastward into the marine deposits, are sub- 

 jects of great interest. Too little is known regarding them, but there is 

 no doubt that the enormous matrices were cut out previous to early 

 Pleistocene time, or at least as far back as the Pliocene. Aggradatioual 

 deposits of Pleistocene age now fill these valleys inland far up the stream- 

 ways towards their headwaters. The great swampy valley of the Atrato 

 of this character is nearly 500 miles in length, having perhaps one of the 

 longest tidal reaches in the world. 



The statement of Upham, 1 Spencer, 2 and others, that Maack found 

 marine Pleistocene fossils at great heights on the Isthmus is erroneous. 

 Their conclusions were based upon Maack's allegation that Pleistocene 

 marine fossils were found on the divide. The locality given is on the 

 Caribbean side, and the fossils collected have since been shown to be 

 Tertiary. 



The great upland lakes of Central America, including the old drained 

 lake beds of Costa Pica and possibly of Panama, most probably date 

 back to the early Pleistocene epoch, but these phenomena indicate 

 land conditions rather than marine. Cope 3 has recently described an 

 extinct bovine (Bos scaphoceros) of undoubted Pleistocene age from 

 these deposits in Nicaragua. The same species, as determined by Mr. 

 F. A. Lucas, has recently been found by me in the Equus beds near 

 Austin, Texas. 



dlastrophism and yulcaxism of the tropical american 

 Mainland. 



The building xip of land by various processes of elevation, and the 

 levelling of the surface by erosion, afford important data for tracing the 



1 American Geologist, Vol. VI. p. 896. 



2 Bull. Geol. Soc. Am., Vol. VI. p. 125. 



3 Journ. Acad. Nat. Sci. Phila., Vol. IX. p. 487, 1894. 



