Mr. Ruhm is one of the pioneers in the phosphate field and his
paper on this subject is the work of an expert.—Ed.
The phosphates of Tennessee occur chiefly, in fact, almost entirely, in
the strata representing the Silurian and Devonian geological ages, or,
more properly, in the former, and in a transition period between the two.
The Silurian age was essentially the age of shell fish, animals with
their skeletons entirely on the outside of their bodies. The deposits of
countless millions of these shell fish and their remains form the immense
beds of limestone representing the Silurian age. The composition of these
shell fish was carbonate of calcium, or “lime,” and hence our common
limestones are calcium carbonate.
[Illustration: _Fig. A._ _Fig. B._]
The Devonian age was the age of fishes or vertebrates, and owing to the
need of greater elasticity of their bones and smaller weight, they are
composed of phosphate of calcium, or “lime.” Far back in the Silurian
age the “Hand that fashioned all things well” began to change some of
these shell fish to provide for the future order of things, so that
their outside skeletons, or shells, were composed of phosphate of lime
instead of carbonate. These two commingling, the resultant beds of rock
became somewhat phosphatic and formed the “phosphatic limestones”
of the Silurian age. In some places the phosphate shells were in
considerable proportion, and subsequent erosion, proper underground
drainage and leaching, dissolved out the carbonate of lime to greater or
less extent and left the “brown phosphate” of the middle basin, varying
in grade according to the preponderance of phosphate shells in the
original deposit and the extent of the subsequent leaching. Meantime the
transition stage between the two ages had been reached and the resulting
deposit spread over the central basin and the highland rim in the form
of a thin blanket of varying thickness and quality of the so-called blue
rock, which is blue, brown, gray and black, according to the coloring
matter present or absent, composed of a preponderance of microscopic
shell fish with skeleton composed of phosphate of lime, but mixed with
enough carbonate to make the resulting mass vary from sixty-five per cent
to as high as eighty per cent calcium phosphate.
The subsequent depression and deposit of Devonian shales and
subcarboniferous beds and subsequent great pressure hardened all these
into rock, and about the middle of the subcarboniferous age all these
were elevated above the surrounding country, and while the rest of the
land was taking its turn in being formed under the seas, this old central
basin was undergoing the wear and tear of erosion that finally produced
the “Dimple of the Universe,” surrounded by its chain of hills and ridges
and flatwoods of the highland rim.
In the central basin where conditions were favorable the intervening
strata between the blue rock and the phosphatic limestones that were
being converted into “brown rock” were sometimes partly and sometimes
entirely washed away, and the blanket of the blue rock, cracked and
broken into plates of the hardest and most durable parts, settled down
on the brown rock, sometimes resting directly on it and sometimes with a
clay seam left to represent the former intervening strata.
A glance at the illustrations will show the process. Let Figure A
represent the deposit as it originally was before the erosion and
leaching started in.
No. 1 represents the layer of blue rock in its original position; 2
the layers of limestone underneath; 3 the layers of highly phosphatic
limestone in suitable condition for leaching; 4 the hard, insoluble
portions of the limestone, and 5 the soluble portions of the limestone,
nonphosphatic.
In Figure B, No. 5 has dissolved out and disappeared. In No. 3, the
carbonate has leached out and it has separated into laminations and
falling into the places left by No. 5, has assumed the jumbled condition
found in the dips between lime boulders; No. 2 has dissolved down to
the clay seam so generally found, varying in thickness from one or two
inches to two or three feet, and No. 1 has settled down conforming to the
general bottom of 3 or top of 4, forming the top rock generally prevalent
in the brown rock field.
If the analysis of the original phosphatic limestone was, say, 50 per
cent phosphate of lime, 38 per cent carbonate and 12 per cent insoluble,
and other matters, and the leaching took out all the soluble carbonate,
the resulting mass would be 80 per cent phosphate, which is generally
the analysis of the bottom rock at Mt. Pleasant, or the “export,” as it
is termed. The top rock varies in analysis from 65 to 80, just as the
original blue rock did.
In the highland rim this process took place only on the slopes of the
narrow creek valleys and occasionally in projecting points, instead of
over large areas of country as in the central basin.
In the portion of the highland rim left intact the blue rock remains
in place as a general thing with its varying quality and thickness,
retaining its original compact form and density.
Occasionally, however, is found the layer of blue rock resting
immediately on the layer of phosphatic limestone, and where this is the
case numerous faults and dips occur, showing a similar structure to the
Mt. Pleasant formation typified.
Again, in the central basin or brown rock region, the top erosion first
disintegrated and then partially took off the upper layers of shale or
flint, sometimes entirely, sometimes leaving it from one to forty feet
thick, which accounts for the varying overburden.
In some places the limestone layers were entirely soluble or reduced to
clay and some acid condition of soil water dissolved the upper layers
of phosphate and redeposited it in the boulder and stalagmite forms of
the “white rock” found in Perry and Decatur counties and near Godwin, in
Maury County, and the “boulder rock” found everywhere to greater or less
extent but in especially heavy deposits near Nashville on the McGavock
Place. These latter redeposit varieties vary in analysis from 50 per cent
to as high as 90 per cent phosphate, and are uncertain as far as the
general variety goes, though individual deposits varying in extent from
one to twenty or thirty acres, are found of very uniform quality.
The first phosphate rock discovered in Tennessee was the kidney formation
that almost always attends the blue rock and black shale deposit. The
eminent physician, naturalist, botanist and geologist, Dr. Gattinger, of
Nashville, of revered and beloved memory, was first to recognize these as
phosphate rock, but being much more interested in determining the family
and pedigree of some new beetle or plant than in the commercial aspect
of any mineral proposition, he never gave his discovery to the world,
and only by his casual mention of the fact one day to Will Shirley and
Maj. W. J. Whitthorne, of Columbia, are we able to give him credit for
the knowledge. Dr. Safford, in his “Geology of Tennessee,” describes in
detail both the blue and brown rocks geologically, referring to the blue
rock as a blue fossiliferous limestone nearly always occurring under the
Devonian shale; but no chemical investigations being provided for, he
did not find out that it was a phosphate rock. Major Whitthorne and Mr.
Shirley kept up a systematic hunt for a deposit of commercial value and
finally the former located one on upper Swan Creek simultaneously with
the discovery made lower down the same creek by Messrs. Bates and Childs.
These latter gentlemen were insistent that the black shale, commonly
called slate rock, so abundant in the highland rim country, was a form
of, or indicative of the proximity of, coal, and at regularly recurring
intervals they would send in particularly promising looking samples to
Professor Wharton, of Nashville, for analysis. One day they dropped into
their bag of samples a piece of blue rock which they informed Professor
Wharton was nearly always present under the “slate,” and seemed to be a
“bloom.” What was their astonishment to receive from Professor Wharton
the report that their coal was still worthless, but that their bloom was
phosphate rock, analyzing over 70 per cent. This was in December, 1893,
and like the news of William Tell in Switzerland, of old, “From hill to
hill the summons flew,” and the whole country went phosphate and option
mad.
Lack of transportation and timidity of capital, coupled with the
large amount of territory occupied by the deposit and the numerous
parties holding properties caused the development to be spasmodic and
comparatively small and scattered, and in consequence the price soon fell
from $4.25 per ton f. o. b. Aetna, which was the first sale, made by the
old Southwestern Phosphate Co., to $2.25 per ton, which was the price at
which blue rock guaranteed 65 per cent was sold in 1896, being just a
small margin over the cost of production and hauling to the railroad.
In January, 1896, at a time when negotiations were on foot for the sale
of a large tract of blue rock land on Swan Creek, Mr. S. Q. Weatherly,
former county judge, and prior to that county surveyor of Lewis County,
while on a trip to Mt. Pleasant, noticed the peculiar brown rock in the
ditch at the roadside on the W. S. Jennings’ farm west of Mt. Pleasant,
and being interested in minerals, picked up a piece of it. Noticing the
analagous appearance to the weathered blue rock, which is generally
brown on the surface, he dropped it in his buggy. On his return to Swan
Creek, he showed it to Mr. Harry Arnold and Col. D. B. Cooper, who were
interested in the negotiations above mentioned. These gentlemen had it
analyzed and finding it to be 75 per cent phosphate rock, induced Mr.
Weatherly to say nothing about it until after their deal was consummated.
Associated with these gentlemen was also Mr. W. J. Webster, and during
the time from January to July, 1896, when the negotiations for the
sale of the blue rock properties were finally closed, they ascertained
partially the extent of the Mt. Pleasant brown rock field.
When their “big trade” was made they formed the firm of H. I. Arnold
& Co., bought two and one-half acres of land from Mr. Mumford Smith,
ostensibly for a calf lot for Mt. Pleasant’s present genial mayor, Mr. W.
D. Cooper, leased at a royalty of ten cents per ton a few acres from Mr.
Cooper and a few from a darky named Tom Smith, got an option from Mrs. M.
G. Frierson on the present Columbian & Blue Grass Hills, and commenced
mining rock and putting it on the cars at a cost of about eighty-five
cents per ton. This rock, without preparation, ran 75 per cent instead of
65 per cent, but whereas the blue rock had never run higher than 3 per
cent I. & A., this rock ran, in the state they shipped it, from 4½ to 6
per cent I. & A.
Of course the manufacturers had bought blue rock for $2.25, and knew they
were getting it at very nearly the cost of production, and when they saw
the “snap” the miner had, they took the stick this excess of I. & A.
gave them and proceeded to beat the price down with it until $1.25 and
eventually $1.00 per ton were common prices.
Capitalists were rendered more timid than ever before, and even astute
phosphate man that he was Col. D. B. Cooper threw up both hands and quit.
He said, “Boys, if that is phosphate, the whole basin of Middle Tennessee
is full of it, and it will never be worth mining, as every farmer will
pick it up off the ground and haul it to the railroad.”
Mr. John S. O’Neal, in a paper presented to the Engineering Association
of the South, as late as 1897, said, “the owner of a bed of phosphate
rock, is not as well off as the owner of a sand bank, given the same
proximity to market.”
The poor fellows in the phosphate business, however, couldn’t get out,
and kept digging away, until gradually capital decided it was worth
buying the lands after all, and as a result nearly $2,000,000 has been
paid for property in the Mt. Pleasant field, about $500,000 in other
portions of Maury County, and over $1,000,000 for property in the
counties of Decatur, Perry, Lewis, Hickman, Giles, Williamson, Davidson
and Sumner. Rock has gradually advanced in price until now 65 per cent
blue rock sells at from $2.60 to $2.80 per ton, 75 per cent brown rock
at from $3.10 to $3.60 per ton and 78 per cent domestic (4½ I. & A.) at
$3.75 to $4.00, while 78 per cent export rock with 3 to 4 per cent I. &
A. sells for from $4.00 to $4.25 per ton.
As the prices have increased the cost of production has increased for one
reason and another, until now each ton of phosphate rock put on board
the cars represents an average cost in labor and salaries of $2.00 per
ton. The production for 1904 having been 540,000 tons, the wage earners
of Tennessee have profited by this industry to the extent of $1,080,000
during last year alone. On the other hand, fertilizer factories have
sprung up all through the interior of the country like magic, and as
they now get 75 per cent rock at their factory for less than the freight
they used to pay on 62 per cent rock from South Carolina, acid phosphate
is cheaper than ever before, and consequently the farmer gets cheaper
fertilizer or else better fertilizer for the same money.
The first thing which impresses itself on the mind of almost any visitor
to the phosphate fields is the almost universal dependence on hand labor
of the simplest pick and shovel kind. This is partially due to the fact
that they “just started that way,” and hence the most “experienced
laborers” have always done that way; and partially to the fact that after
sufficient capital was at hand for the purpose, the varying conditions
met with in the deposit made it very difficult to devise appliances
suitable for one portion of a mine that would answer the requirements in
the closely adjacent portions.
For instance, it is possible in the same open face of a mine to find the
overburden varying from two feet to twenty and the rock from a few inches
thick, sticking tight to the top of a lime boulder, to fifteen feet in
the “dip between two boulders,” while the rock itself will vary from the
shaly, partially disintegrated top rock through various sizes to heavy
blocks six to eight inches thick and often ten or twelve feet long.
It will therefore be seen how difficult it is to design a machine that
will accommodate itself to the handling of this material. The removal of
the overburden has been generally accomplished with wheel scrapers. Two
companies have used the New Era or Western machine plow with elevator
belt loading the dirt into dump bottom wagons alongside. Two steam
shovels are now in use, being of the traction type, and occasionally
these have been used in digging the rock, though apparently with not
sufficient success to justify its continuance. Cableways have never been
used to transport the material and this is done largely by wagon and
team, though many tram roads with cars propelled either by mules or dinky
engines are in use.
The bulk of the rock, however, is dug by the miner with pick and fork,
loaded into wagons, hauled out and dumped in windrows on the ground,
stirred with a potato plow and harrows, allowed to dry in the sun, taken
up again into wagons and hauled either direct to cars for shipping
or put under sheds for storage. When an extra good quality of rock is
wanted, as for export, a few layers of cordwood are put down and the
sun-dried rock put on that. Then, when ready to ship, the wood is fired,
and after the rock is cool, it is broken and loaded with forks, when most
of the dirt sloughs off, leaving the rock almost perfectly clean.
Some rock can be put from the mines immediately on the wood and burned
for export, but generally this will only be a safe domestic rock. Some
companies who have water accessible, pick out the large pieces and send
them direct to the dry kilns and then the small pieces with the dirt,
known as “muck,” are passed through washers, the rock coming out clean,
and being deposited on cordwood and burned as above described.
The resulting rock, after being crushed, is passed through screens which
separate it in three sizes, from one and one-half inch up going for
export, between that and one-fourth inch for domestic, and the dust and
one-fourth inch pieces being ground up and sold for direct use or to
small factories.
The Century Phosphate Co. has installed a system of dryers and do not
wash the rock, but dry it thoroughly in mechanical dryers and then screen
and separate it as above.
The reason the larger pieces are as a rule of higher grade than the
smaller, is that the dirt and impurity is mostly on the surface of the
rock and the greater the proportion of surface to volume the lower the
grade in B. P. L. and the higher in iron and alumina.
Owners and operators of mines are gradually turning their attention
to labor-saving devices for primary operations, and for systems of
reclaiming the immense amount of waste that has heretofore gone on, both
in the mining and the preparation of the rock.
One marked step forward in the business is the establishment of a
small mixing plant for making complete fertilizers, and the commencing
of operations on a large acid phosphate factory, with prospects for
additional ones later on.
At least ten per cent of the present output is thrown away to prepare
the high grade rock necessary, and this waste will make good 13 per cent
acid phosphate, so that every year 50,000 tons of valuable material is
absolutely thrown away. This is more phosphate rock than is annually
used by any one fertilizer factory in the world, so far as known to the
writer. This waste product could easily be transported to a local factory
for an average cost of less than 50 cents per ton. Sulphuric acid can be
bought laid down at Mt. Pleasant for $7 per ton. The mixing and other
preparation will not exceed $2 per ton, so that using half acid and half
rock the cost of the acid phosphate will not be more than $4.75 per ton,
while it will probably sell for at least $8 per ton. From these figures
we appear to be throwing into the waste pile at present material that
should represent a profit of not less than $162,500 per annum. That
this will be allowed to continue does not appear likely. The question
might arise, however, “What will you do with the acid phosphate thus
manufactured to keep from overcrowding or at least injuring the market?”
I should answer this by calling attention to the immense area of land
in Maury, Lawrence, Lewis and Hickman counties, known as “The Barrens,”
which are gradually being denuded of their timber for cordwood that is
shipped to Mt. Pleasant for use in drying the phosphate rock. There are
at least 250,000 acres of this land, which is now readily purchasable
at $3 per acre, with the cord wood on it. The wood alone will yield in
value more than this price, thus leaving the land clear. Now, it has been
demonstrated at Lawrenceburg, Summertown, Loretto, St. Joseph, Hohenwald
and numerous other places that systematic and intelligent farming, even
with the meager supply of fertilizer (almost entirely in the shape of
bone meal) that has been used, will bring these lands up to a point
where they will bring from fifteen to twenty bushels of wheat or from
twenty-five to thirty bushels of corn per acre. Such lands that have been
so brought up readily sell for from $10 to $40 per acre, according to
location.
From experiments it has been ascertained that the principal element of
plant food lacking in these soils is phosphoric acid. The application
of 275 pounds of acid phosphate per acre each year on these lands would
consume right at our doors the entire output of the proposed acid
factory, even if none were sold elsewhere. This appears chimerical to
the casual observer, I must confess, but a careful investigation will
demonstrate the soundness of the position taken.
A feature throwing some light on the development of the business at Mt.
Pleasant is shown by the following table:
The lengths of track built in each year are as follows: