204. S. W. Ford—New locality of Primordial 
farther north I followed the Miocene the less disturbed I found 
it. Kast of the volcano of Turrialba I found Miocene, with 
line of voleanoes, Turrialba, Irazu, Barba, and Poos covers all 
the other rocks; but on the west face of the Aguacate Moun- 
tains, where the coating of ash is in places absent, we find highly 
altered claystones. These are rich in mineral veins, and have 
been thoroughly explored for mines of gold and silver. Whether 
the rock is the ancient clay slate from which the conglomerates 
were formed, or whether it is highly metamorphosed Tertiary, 
we have, as yet, no means of knowing, and the problem wi 
require careful study for its solution. 
Costa Rica, Nov. 29, 1874. 
Art. XXIV.—WNote on the Discovery of a new locality of Primor- 
dial Fossils in Rensselaer County, N. Y.; by S. W. Forp 
thickness of the above enumerated beds cannot here be givel 
with exactness; but that of the thin saudstones is not far from 
thirty feet, and that of the superposed slates and shales about 
twenty. The heavy-bedded sandstones are of much greater 
extent. At one point they form a sharp, bold elevation, — 
locally known as “Diamond Rock.” All of these beds are 
arranged in a series of close synclinal and anticlinal folds 
