HILL: GEOLOGY OF THE ISTHMUS OF PANAMA. 245 
that, with the exception of the northern half of the peninsula of Yuca- 
tan, which is composed of them, and in Florida, formations of this char- 
acter are strikingly absent along the immense stretch of the coastal region 
of the Gulf and Caribbean mainland. These sea derived formations are 
chiefly of Vicksburg Eocene, Oligocene, Pliocene, and-recent origin. 
Land Derived Littoral Deposits. — These are essentially composed of 
thinly bedded land débris, — sands and clays, usually unconsolidated, 
occurring in numerous thin stratigraphic alternations. The accessory 
conditions are the accompaniment of much ferruginous material, espe- 
cially iron in the shape of pyrites ; and impure lime derived from solu- 
tion of fossil shells, and the percolation and redeposition of the same. 
This lime as it occurs is a secondary product, and is never of chalky 
texture. It is nearly always more or less arenaceous, argillaceous, and 
ferruginous,  Lignite and leaves and stems of plants also occur often 
in great abundance. This character of sedimentation is indicative that 
land existed in close proximity from which the deposits were derived, 
and near which they have been laid down in a comparatively narrow 
belt. 
The Kocene and Oligocene deposits of the whole of the Atlantic Gulf 
and Caribbean continental borders are largely of this character. These 
impure alternating littoral land derived deposits compose nearly all of 
the lower Tertiary formations bordering the Atlantic side of the North 
Central and South American continents from New England to the east 
of the Gulf of Maracaibo, and follow the bordering islands thence to 
Trinidad. Analogous formations are now being made along the ocean’s 
margin within the limit of coastal sedimentation. We think that no geol- 
ogist will deny that the proximity of marginal land accompanied the depo- 
sition of formations of this character, and that the existence of this land was 
as certain as that of the formations themselves, 
With the exception of the doubtful Empire limestone, Tertiary forma- 
tions of the first mentioned class, sea derived formations do not occur 
in the Isthmian region. 
The Older Tertiary Littoral of the Gulf and Caribbean, — There can 
be no doubt of the occurrence around the Caribbean perimeter of a con- 
tinuous fringe of the older Tertiary littoral formations of the second class 
mentioned from east of the Mississippi to the Gulf of Maracaibo, that 
these formations are largely of Eocene and Oligocene (older Miocene) 
age, and that they are genetically related to, continuous with, and the 
product of the same processes as those formations of the Caribbean side 
of the Isthmus and Costa Rica described in this paper. 
VOL. XX VIII, — NO. б. 7 
