Ko. 275.] 
1&7 
1. Mesotype. In cavities and veins in greenstone* 
2. BaiholUe. From the same source* 
3. A'po'phylliie* Also from same source. 
4. Chlorite. Same source, found in small quantities. 
All of this last class have been found in small quantities in veins in 
the boulders of greenstone, barely sufficient to determine their charac- 
ters. 
VII. 
Diluvial grooves and scratches. 
From the preceding remarks on the transported materials of the is- 
land, and from observations on the geology of the vicinity, it is quite 
certain that an immense force has been in action at a former period and 
has carried a vast amount of mineral materials from their original beds, 
and spread them over a large area. That water was in some way the 
agent is the united opinion of geologists, but the circumstances attend- 
ing it, the immediate cause or causes of its movement, and the precise 
epoch in w^hich it took place, it would be difficult, if not impossible, in 
the present state of our knowledge, to determine. 
My remarks will therefore be confined rather to the force and direc- 
tion of the current than to the causes which produced it. 
The direction of the current is ascertained by that of the grooves and 
scratches left on the solid rocks ^ and its force, by the size and quanti- 
ty of the fragments, and the distance and elevations over which they 
have been transported. 
The term grooves, as here used, applies to all the furrows that are an 
inch or more across; the term scratches to all those less than an inch 
across; the word furrow without reference to size, but as a general term. 
Diluvial grooves and scratches have been found in every section of 
the island, from 16th-street on the south, to SOOth-street on the north, 
(or to the southern termination of the limestone,) and from the banks 
of the Hudson on the west, to Harlem river on the east. 
The furrows generally are most distinct where the rock has been re- 
cently uncovered; and least so where it has long been exposed to the 
action of the elements. They have been found on the highest rocks, 
and at the lowest tide water marks, being a difference of more than 100 
feet perpendicular height. It is evident, therefore, that if these fur- 
rows were the result of a single diluvial action^ or a single deluge, the 
