Mo. 200.J 
149 
Rider's Pond was also supposed to contain it, though for the same 
reason it was not examined. 
Mr. Prescot, of Hillsdale, informed me of two beds of marl in that 
town. One is on the lands of Mr. Mitchell and Judge Loop. This 
marl has been used on corn, instead of plaster of Paris, by Mr. John 
Chapman, and found to answer the purpose equally well. The 
other locality is a pond on Mrs. E. Burton's farm, near the Co- 
lumbia turnpike. These marls are filled with fresh water shells. The 
first mentioned of these two deposits is covered by peat about two feet 
in depth. 
The value of fresh water shell marl is well known to our intelligent 
farmers; but few know it when they see it, and still fewer know in 
what situations co seek it. For these reasons, I have particularized its 
characters, its situations, and some of its localities. It performs the 
same office on the land as air slaked lime, and is as valuable a ma- 
nure, while it has not its causticity to injure vegetation. One object in 
burning lime for land is, to reduce it to the state of powder by slaking. 
The shell marl is already in a pulverulent state, and only requires to be 
dug from the swamps and ponds and spread on the land. 
It is supposed that the above localities do not embrace one half of the 
quantity of this shell marl in Columbia and Dutchess counties, and it is 
'probable that it may be found in every township. The extent of coun- 
try which it was necessary for us to examine during the past season, in 
order to accomplish the geological survey in the time contemplated by 
the Legislature, rendered it impossible to visit, much less to examine, 
more than a small part of the localities where the marl, peat, marble, 
&c. &c. might be expected to occur. 
The shell marl may be used to replace gypsum, or at least, a part of 
it, of which there is a great consumption. Gypsum has been invalua- 
ble to the lands of these counties, and it is probable that the shell marl 
deposits will be of as great a value to the farming interests. It is esti- 
mated that the quantity of gypsum consumed annually in Columbia and 
Dutchess counties, amounts to from 15,000 to 30,000 tons. This is 
imported from Nova Scotia, and delivered at the wharves on the Hud- 
son river at about $5 per ton. Allowing the consumption at 20,000 
tons, the sum expended annually, exclusive of that for interior trans- 
portation, and the grinding, amounts to $100,000. 
