ALLUVIAL DIVISION. 
11 
marl. Shell marl is a white pulverulent substance when dry ; and when wet, is so soft that 
a pole may be easily thrust into it. It is composed of the shells and decayed fragments of 
the Lymnaea, Physa heterostropha, Planorbis trivolvis, P. campanulatus, Cyclas similis, and 
some other species. Uniones and anodontae are sometimes found in it.* 
Many of the beds of shell marl are covered by beds of peat from two to ten feet thick. 
Such localities were once lakes or ponds, which have been gradually filled up with alluvial 
depositions, and become land. The marl, if present, may be found by thrusting a pole through 
the mud into the stratum below ; on withdrawing it, the marl may be recognized as a white 
slimy mud on the lower part of the pole, more or less concealed by the black mud through 
which it has been withdrawn. In some parts of Orange and Dutchess counties, this marl is 
much used by the farmers, and with great advantage to their crops. It is also used some in 
other counties along the Hudson, but its value is not yet fully appreciated. It is desirable 
that agriculturists should make more extensive use of a manure so valuable as this, on soils 
that contain little lime. This mineral may also be used, when pure, for whiting, and for 
making lime. 
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 to seek it. For these reasons, I 
have particularized its characters, its situations, and some of its localities, in the table of 
localities of marl and peat. It performs the same ofifice on the land as air-slaked lime, and 
is as valuable a manure, 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 localities mentioned in the table do not embrace one-half of the 
quantity of this shell-marl in the counties along the Hudson above the Highlands, and it is 
probable that it may be found in every township. The extent of country which it was neces¬ 
sary for us to examine, 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 various useful materials 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 invaluable to the lands of the counties above the High¬ 
lands, and it is probable that the shell-marl deposits will be of as great a value to the farming 
interests. It is estimated 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 Hudson river at about five dollars per ton. Allow¬ 
ing the consumption at 20,000 tons, the sum expended annually, exclusive of that for interior 
transportation, and the grinding, amounts to $100,000. 
♦ Piles of these bivalve shells are sometimes seen on the edges of the marl banks, and on the shores, that have been carried 
there by the muskrats, to devour the testaceous animals. 
