No. 200.] 169 
cify particular localities of these clays, as they form the surface, or un- 
derlay the gravel beds of the plains of Columbia and Dutchess counties; 
and these plains probably form one-eighth of their whole area. Their 
thickness varies from a few feet to 100 or more,* so that they are per- 
fectly inexhaustible, and offer means of profitable industry to many 
thousands for an unlimited period of time. 
Clay stones, as they are called, are found abundantly in many loca- 
lities in the upper beds, within fifteen feet of the surface. They are 
also called indurated clay. They assume a great variety of imitative 
forms, and nearly all of them have a hole through the centre, from the 
size of a pin to three or four inches in diameter. Some geologists have 
supposed them to be fossil remains. Their origin has been long known, 
however, to some of the people of the Hudson valley, where they may 
be seen in all stages of their formation. They contain more carbonate 
of lime than the surrounding clay, and enough to indurate it. They 
never occur here at greater depths than the roots and fibrous rootlets of 
plants and trees penetrate. The calcareous matter in solution in the 
water, is deposited in the clay around the rootlets, while the water is 
absorbed and serves to nourish the plants. 
These clay stones are important in an economical view^, for if not 
separated from the clay in the manufacture of bricks, during the burn- 
ing they are converted into lime. When the bricks become moist- 
ened, either by exposure to the weather or by laying in mortar, this 
lime slacks and bursts them in pieces. 
Coarse pottery is manufactured from the clays of Columbia and 
Dutchess counties, but it is a branch of industry in which little capital 
and fiew persons are employed. 
Brwks. 
The following table shows the amount of the brick manufactured in 
Columbia and Dutchess counties: 
At Stuyvesant there are four brick yards, at which are made annually 
from 1,500,000 to 2,000,000. 
* The following section obtained by Mr. Disbrow, in boring for water at Hudson, eliews the 
the thickness of the clay at one point. 
Feet. 
Clay, 144 
Sand, 40 
Hard pan, 30 
Gravel, 4 
Slate Rock, 
218 
He penetrated seventy feet into the slate rock without observing any change in its character, 
[Am, Jour, of Science, xii. p. 139.] 
