W. M. Gabb—Notes on Costa Rica Geology. 201 
tion. On the upper part of the Coen River, on one of its largest 
western branches, 1 found a single small boulder of mica slate, 
but I could not trace it to its source. 
only over the greater part of Talamanca, but also farther north 
and northwest, in the adjoining parts of Costa Rica. These 
prove, beyond a reasonable doubt, that the rocks are an exten- 
sion of the great Miocene deposit found not only on the isthmus 
proper, but over so many of the West Indian islands. I re- 
cognized at sight many familiar species, and have no doubt 
that others only await comparison to identify them with known 
ecies. 
These Miocene rocks are made up principally of conglomer- 
ates and fine shales, with occasional beds of sandstone, and a 
very little limestone. The limestone occurs most abundantly 
in the central regions of Costa Rica, in the Candelaria Moun- 
tains, and on the Reventazon River near Sapote, and are almost 
entirely wanting in Talamanca. The conglomerates and shales 
are also found as far as the latter locality; while the last men- 
tioned rock is the most important constituent of the Candelaria 
range. Wherever the shales are found unaltered, they carry 
small beds of very inferior coal. It is to this member that the 
coal mines of Chiriqui belong: and, half a dozen miles south 
of San José, the capital of Costa Rica, there is a small mine of 
coal now being worked experimentally, with results far from 
n 
. 
encourag . 
