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. Тһе 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 aggradational 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. Aggradational 
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,! Spencer,? 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 
Jaribbean 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 Rica and possibly of Panama, most probably date 
back to the early Pleistocene epoch, but these phenomena indicate 
land conditions rather than marine. Cope? has recently described an 
extinct bovine (Bos seaphoceros) 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. 
DrAsTROPHISM AND VULOANISM OF THE TROPICAL AMERICAN 
MAINLAND. 
The building up 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. VT. p. 396. 
2 Bull. Geol. Soc. Am., Vol. VI. p. 125. 
8 Journ. Acad. Nat. Sci. Phila., Vol. IX. p. 487, 1894, 
