VoL. f Y. 
AUGUSTA, GA., JUNE, 1846. 
No. 6. 
A LETTER ADDRESSED TO THE AOKrCULTUEAL SO- 
CIETY OF JEFFERSON COUNTY, GA. 
BY J. H, HAMMOND. 
Dear Sm .'—I embrace the earliest opportuni- 
tY my other engagements haYe allowed me, of 
fulfilliag my promise to compfy ^ith the re- 
quest of 3 ''oar Society, to give them such infor- 
mation as I possess in regard to Marl. I am 
happy to learn that an interest in this matter has 
bean excited in your county, and if in what I 
am about to say, I shall fail to meet all the in- 
quiries which might be made, .t will afford me 
great pleasure to communicate more fully on 
particular points, at any timi^ereafier. 
Aware of the strong pre^dice existing tSo 
generally aiiiong farmers against everything 
neio in farming, it may not be amiss for me to 
begin by sa 3 'ing, that however new to us marl- 
ing may have been a few years ago, it is in 
point of fact one of the very oldest agricultural 
operations ol which we have any authentic re- 
cord. Pliny, who wrote during the first century 
of our era, mentions marl ns having been long 
in use among the Greeks and also in Gaul and 
Britain. He describes pretty accurately the ap- 
pearance of all, or nearly all, the kinds of marl 
now known. He even specifies the peculiar 
effects of each on sods, and states the length of 
lime these effects were supposed to last, which 
was from 10 to 80 years, according to the qual- 
ity of the marl and the Ihnd marled. Varro, 
who wrote a century belore Pliny, mentions 
having seen fields in Gaul covered with a 
“ white fossil clay,” and also describes several 
varieties of mar! as in common use. 
Although these writers, because ignorant of 
the discoveries of modern science, make great 
blunders in attempting to account for the extra- 
ordinary influence exertet! by this earth on vege- 
tation, and to discriminate between its varieties, 
still it is unquestionable that the ” leucar^Ulon" 
of the Greeks, the fossicia crela’’ of Varro and 
the ‘^marga” of Pliny, were no other than the- 
same kinds of marl we find here, and which at 
this day so many enterprising farmers, both in 
Europe and America, are actively and exten- 
sively engaged in spreading over their fields, 
and which have been continuously used for 
that purpose more or less from the remotest 
ages. Marling, then, is certainly no novelty — 
no untried experiment, than can for a nao.ment 
be classed among modern humbugs. 
There is no question, however, that the want 
of chemical knowledge has in time past led to 
great errors in its application and consequent 
failures— often to serious injury from its use. 
When the element in marl which gives it its 
chief virtue, and also its certain and its proba- 
ble ch.einical action on the soil and its growth, 
were all unknown, every new application of 
it was to some extent an experiment which 
might or might not succeed. It is a great proof 
of its universal value, that so many succeeded 
as to maintain its reputation and consequent 
use. Mr. Rufiin, of Virginia, was the first in 
this country to explain on scientific principles 
the true nature of marl, its mode of action, and 
the proper manner of applying it, and to carry 
his theory through the oideal of successful ex- 
periment. He is the founder of the marling 
system among us, for which he will be long 
and deservedly ranked among public benefac- 
t»ns. His “Essay on Calcareous Manure,” 
contains every thing that it is important to 
’ know about marl and marling. Throughout 
my operations, it has been my guide, and it is 
still, I believe, far in advance of anything that 
has yet been published in any country on the 
subject. If I thought every member of your 
Society would procure a cop 3 ’’ of that Essay, 
and peruse it carefully, I might close my letter 
here, by earnestly recommending them to do so. 
It is with the hope of inducing some of them to 
do it, as well as to testify my respect for them, 
by responding to their inquiry, that I proceed. 
Marl, as correctly defined by Mr. Rufiin, and 
now known in this country, is calcareous earth: 
that is, earth containing lime. The lime found 
in it is united for the most part with carbonic acid, 
and is therefore called carbonate of lime. It 
sometimes contains lime in othei combinations, 
as sulphate and phosphate oflirae. Azote, has 
been found in marl also, and magnesia is not 
uncommon. Besides these it contains sand and 
clay in various proportions, and occasionally a 
green sand highly prized as a manure on ac- 
count of itb being rich in potash. All of these 
constituents are valuable to the farmer. But it 
is the quantity of carbon.ate of lime which 
gives its character to Marl, and by which it is 
estimated when it is called rich or poor. 
Nothing is more deceptive in appearance, 
and the most experienced are liable to mistakes, 
if they attempt to estimate its value by the eye, 
and without employing the proper chemical test. 
There is a rock found in abundance in your 
county, and which is of great value for other 
purposes, that has deceived many. It seems to 
be a mass ol shells ; but the fact is, they are on- 
ly effigies, or casts from which every particle of 
lime has been long since washed away, and 
sand deposited in its place. There is also a 
fine, soapy earth, usually of a pale ash colour, 
though sometimes darker, that many have re- 
garded as very rich marl. This is what was 
formerly, and by foreign writers is still, denom- 
inated clay marl. It seldom contains muchlime, 
and is generally wholly destitute ol it even when 
found in marl beds. This soapy feeling is a 
very uncertain indication of lime. Where it is 
observed in marl, it is usually owing to some- 
thing else, chiefly to magnesia or alumina. A 
marl is found whiter and harder than the earth 
to which I refer, but of the 'same larnellaled 
structure and a somewhat soapy touch, that is 
exceedingly rich in lime, — that at Shell Bluff 
containing 90 fnlJ per cent, of the carbonate, 
ft yields readily to the knife, crumbles when 
exposed to a severe freeze, and is altogether 
the most valuable marl we have. Unfortunate- 
ly, it is not met with in large quantities in our 
formation. In our mar! beds immense quanti- 
ties oi large shells are generally found. Inex- 
perienced marlers have been known to spread 
these on their land. But they are ol little or no 
value, unless burned or crushed. They were 
deposited where they are found before the hu- 
man race inhabited the earth, and being for the 
most part sound yet, will yley little or no lime 
to the soil in ourday. Eventhe masses of much 
smaller, conglomerated shells, though very rich 
in lime, are not among the most valuable marls, 
unless broken up and pulverised to a considera- 
ble extent. There is a marl abounding with us, 
which to the naked eye seems to be mere sand, 
that is much more valuable, though it does not i 
contain two-thirds of the quantity of carbonate of 
’ lime; it mixes at once with the soil and exerts 
its full influence in a comparatively short peri- 
od. The most valuablemarl,practica!!yspeak- 
ing, that is found in any quantity at Shell Bluff 
— and will be found in your marl-beds, for the 
formation is the same — is composed of very fine 
shells, scarcely discernable, which are loosely 
cemented together and readily fall apart. It is 
of different colors; mostly^ -white, sometime.s 
purplish, yellow, or light brown. The most a- 
bundant marl found in our formation is hard 
and compact, of a grey color, containing 50 to 
60 per cent, of lime, crumbles on exposure to 
the seasons and in handling. 
But, as! have said, the value ot marl cannot 
be estimated by its appearance. Between eart.i 
which contains 75 per ct. of carbonate of lime, 
and that containing 20 per ct , or even none at all 
the most experienced ai’e far oftener than other- 
wise unable to distinguish without using the 
proper tests. These are so readily to be pro- 
cured, and in fad the analysis of marl, so far 
as to ascertain the qur.ntity of carbonate ot 
lime, is so very simple an operation, that the 
marler she uld leave nothing to conjecture on 
this important point. Earth containing any 
notable proportion of carbonate of lime, will 
effervesce if thrown into vinegar or almost any 
acid. But the best test is muriatic acid : a sin- 
gle drop ot it will produce immediate efferves- 
cence whenever there is carbonate of lime. To 
discover the precise quantity of carbonate of 
lime in any marl, it is only necessary 1 1 
have this acid, a pair of common apotheca- 
ries’ scales with weights, and a wide mouthed 
vial. Dry the marl thoroughly on a shovel 
over the fire, and pound in a mortal, to a 
fine powder. Fill the vial about one-third with 
the muriatic acid diluted with two parts of wa- 
ter to one of acid, and. balance it exactly in the 
scales, with weights o* any kind. Then add, 
very slowlyq 100 grains of the powder previous- 
ly weighed, taking care not to make it effer- 
vesce so rapidly as to throw any of it out ol the 
vial. When the effervescence has completely 
ceased, blow gently into the mouth of the vial, 
with a common bellows, to expel any of the 
carbonic acid gas which may have remained in 
it in consequence of its being heavier than the 
atmospheric air. Weights to the amount of 
100 grains must now be put in the opposite 
scale to balance the 100 grains of powdered 
marl put into the vial. It will be found that in 
consequence of the escape of carbonic acid in 
a gaseous form, the scale with the vial will 
rise: put weights into it then until the scales 
are once more exactly balanced—the number of 
grains put in the scale with the vial will of 
course indicate the weight of the carbonic acid 
that has escaped. Now, carbonateof lime con- 
tains in 100 parts very nearly 56 parts of lime 
and 41 of carb. acid. It then 44 grains have 
escaped in your analysis, the specimen is pure 
carbonate of lime. If only 2? grains have es- 
caped, then it contains but 50 per cent, of car- 
bonate of lime. And so in proportion to any 
quantity of carbonic acid which may have been 
expelled. In practice, it will be found most 
convenient to use 50 grains of the powdered 
marl. A very few trials will enable the most 
inexperienced farmer to ascertain in half an 
hour with sufficient precision, the value of his 
marl. That value depending mainly, as stated, 
OH the quantity of carbonate of lime it contains. 
The value of lime for agricultural purposes, 
