Marl.
In many of the Tidewater counties enormous beds of blue and green
sand marl and shells are found but a few feet below the surface, supplying
a fertilizing material at a nominal cost, that is rapidly converting all that
region into the garden spot of the continent for supplying the great cities
of the Atlantic coast with table vegetables of the highest excellence, and
is giving much importance to the peanut culture. A full description of
the geological formation of this alluvial region would not be interesting to
the unscientific reader, but it may be well to call attention to the difference
between the marls of the more recent formations, the pliocene and miocene, which derive their value mainly from the carbonate of lime which they
contain, and the green sands and olive earths which are found in the
eocene in conjunction with the shell or calcareous marl. (Green sand is
sometimes found mixed with the marl of the miocene region.)
The region of eocene marls extends from the falls of the rivers eastward
fifteen to twenty miles. Miocene marl is often found overlying the
eocene, and is easily recognized by the difference in the shells which it
contains—scallops and others not found in the eocene. "Beneath this (Professor
Rogers, quoted by Dr. Pollard, says), and usually separated from it
by a thin line of `black pebbles,' like those occurring on the Pamunkey,
there occurs a stratum of greenish, red, and yellow aspect, containing much
green sand and gypsum, the latter partly disseminated in small grains,
and partly grouped in large crystals. The under stratum, rich in green
sand and containing a few shells in friable condition, extends to some
depth below the level of the river. At `Evergreen' the whole thickness
of the deposit appears to be about twenty feet."
This was said of the James River formation, but will apply as a general
description to the deposits of the Pamunkey, Mattaponi, Rappahannock,
and Potomac, as Professor Rogers says "eocene marl is there found
very similar to that on the James. On the Mattaponi the occurrence of
green sand strata has been ascertained in some places, while in others the
beds containing the substance have been replaced by beds of clay, which
are less likely to prove valuable agriculturally. The olive earth overlying
some of these beds, particularly on the Pamunkey, seems to have lost
some of the carbonate of lime which it once contained, and has but a small
portion of gypsum."
The agricultural report for 1888, speaking of Tidewater Virginia,
says: Not only has this section been blessed with lime beds, brought up
by all its streams from the ocean, placing this valuable deposit of miocene
marl at its doors, but the Rappahannock, the North and South Annas, the
James and Appomattox, rising in the felspar and hornblende ridges and
valleys of Piedmont, and the black rock of Buckingham and Appomattox
crossing through the pyrites and sulphur ledge, have brought down the potash
and mingled it with these sulphates, carrying them to meet the tide,
bringing the shells and fossil bones from the ocean. These, and the dead
marine animals and their coprolites, formed the eocene marl beds, where
the sulphates and shells made sulphate of lime (plaster—the great Ruffin's
"gypseous earth"), and the potash and fossils gave the green sand its
agricultural value.
The lands on the Pamunkey and James that were heavily marled with
the Pamunkey and James River green sand, are fertile and productive
today, although for more than twenty-five years they have had neither
manure or fertilizer. These marls have been tested by chemical analysis
and agricultural experience, and the value of Virginia shell marl as an
agricultural lime, and the green sand marl as an active fertilizer, is put
beyond the possibility of a doubt.
There is considerable interest manifested now in the marl deposit
of the State. The value of green sand as a basis for high-grade commercial
fertilizers, and of the carbonate marls and adjacent clays for cements,
has caused extensive investigation. There are works on James River and
the Pamunkey, preparing green sand marl for sale, now in operation with
good profit.
