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 ahsent 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 debris, — 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 Eocene and Oligocene deposits of the whole of the Atlantic Gulf 

 and Caribbean continental borders are largely of this character. These 

 impure alternating littoral laud 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 ivill deny that the proximity of marginal land dccompanied 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. XXVIII. — NO. 5. 7 



