Na 275.] 
79 
while formerly fourteen to sixteen were necessary, where wood alone 
was employed, and the expense is reduced about three-fifths. The bricks 
being somewhat porous, permits the air to penetrate to the particles of 
anthracite diffused through their substance, and the heat is thus applied 
just where it is required, and without loss; and the wood is necessary 
merely to raise the temperature of the bricks to such a point that the 
anthracite shall begin to burn. 
The principle involved in this improvement has been long in use in 
Europe; and in England their brick earth is required by law to be mixed 
with a certain proportion of the ashes of stone coal, which always con- 
tain much coke or half burnt coal, and which during the burning, performs 
the same office as the dust of anthracite, and makes hard burnt bricks. 
Many improvements have been made in the brick manufacture within a 
few years, and they are all in use in the brick yards on the Hudson ri- 
ver. The most important are those for grinding the clay, for moulding 
by machinery, and the one for burning that has already been mentioned. 
At Carpenter's yard, below Peekskill, the grinding and moulding are 
effected by steam power. The clay and sand banks in the clay and ter- 
tiary deposits along the banks of the Hudson, contain the elements of 
wealth and industry w^hich w^ill require a great length of time and the 
most favorable circumstance to exhaust. 
Rocks of New-York, Westchester and Putnam counties. 
The rocks of these counties are numerous, many of them are applied 
to useful purposes, and they are every where abundant, and are seen 
cropping out from the surface of almost every hill and ravine. They 
will be discussed in the following order, viz: 
1. Granite. 
2. Gneiss. 
3. Mica Slate. 
4. Quartz Rock. 
5. Talcose Slate. 
6. Limestone. 
7. Sienite. 
8. Serpentine. 
9. Steatite. 
10. Augite Rock. 
11. Greenstone. 
The metalliferous and mineral contents of these rocks will then be 
described. 
