190 
[Assembly 
There is, however, a prolongation of the Harlem and Manhattanville 
valley, which extends northward and embracing the 8th avenue till it 
strikes the Harlem river at McComb's dam. It consists generally of 
sand and diluvial loam, and is almost a perfect level; few boulders are 
to be seen on its surface, except on its northernmost part, where they 
are found in great abundance. 
V. 
Boulders — iheir sources and abundance in different parts of the island. 
The following are the principal varieties of rock; 
1. Greenstone in all its varieties. 
2. Red and gray sandstone, and their varieties. 
3. Serpentine like that at Hoboken. 
4. White primary limestone like that at Kingsbridge. 
5. Granite and gneiss like that found on the island. 
6. Hydrous anthophyllite like that found in place on the west side of 
the island. 
7. Greywacke like that found in the valley of the Hudson above the 
Highlands. 
8. Limestone like that of the Catskill mountains. 
9. Ferruginous sandstone or jasper rock, like the sandstone underly- 
ing the Palissades near Fort Lee. 
10. Clay stone, supposed to be from the same source as the last. 
11. Actynolite, supposed from the anthophyllite locality. 
12. Kyanite — this has been found in small fragments, but I am not 
aware that it has been traced to its locality. 
The abundance of the several varieties of rock above enumerated, is 
very different in different parts of the island. While some are common 
to every section, others are confined to a particular part; thus, green- 
stone is found in boulders every where from north to south, and from 
east to west, while serpentine, like that at Hoboken, is confined to the 
southern limits. The details of these facts will be found below. 
1. Greei'isione. This in all varieties is perhaps the most abundant rock 
that is not found in place on the island, yet in boulders is common to 
every part of it. In almost every instance, they are worn to a rounded 
form, though it is one of the hardest and toughest rocks known. They 
are among the largest transported rocks on the island, being from 10 to 
J5 feet in diameter, and often covered with grooves and scratches indi- 
