266 GEOLOGICAL SURVEY 
In this kiln the height of the arch is peculiar, as may be seen in 3. This is constructed, as 
represented in the section, by allowing each layer of the stones to project a little, at the same time 
that the back is built up; otherwise, of course, the whole would fall. This vast furnace is filled 
with wood, thrown in through the door-way, which is immediately closed. From forty-eight to 
sixty hours are required for the burning of such a charge as this kiln holds. 'Two men are em- 
ployed constantly, who, during the operation of burning, relieve each other. 
As there is a certain waste of fuel inseparable from those kilns that require to be cooled down 
after each charge, perpetual kilns have been invented to obviate this defect. In such kilns the lime 
is drawn below, and a fresh charge thrown in above, at the same time that the firing is kept up, 
without intermission, Of course such kilns are only required where the demand is constant. 
Fig. 38 is a section of a perpetu- 
al kiln. With the exception of the 
furnaces on each side, it differs lit- 
tle from the ordinary kiln. It is put 
in operation by first filling that part 
bclow the fire-places with layers cf 
wood and limestone, whith are fired 
and burned. Upon this the broken 
limestone is piled up, till the kiln is 
full. The furnaces are next set in 
operation ; and when the limestone 
has been subjected to the heat fora 
sufficient length of time, the burn- 
ed lime below is drawn through a 
hole, left for the purpose, which al- 
so serves as an air-hole. The top 
of the charge, of course, sinks, and 
fresh limestone is thrown in. The 
quantity of lime taken at each 
drawing is learned by a little ex- 
7 
i oe eS 
perience. The drawing explains the rest. 
Lime is burned, in New Hampshire, at seventy-five cents per tierce: the tierce is said to contain 
six bushels. At Thomaston, a cask of lime is delivered on the wharf, for seventy cents. 'The 
price of the empty cask is forty-two cents; and that of wood varies from one dollar to four dollars 
and fifty cents per cord. The limestone of South Carolina is so situated that wood costs compa- 
ratively little, yet the market is supplied from the North. C 
The little lime that is burned in the State is sold, at the kiln, at twenty-five cents per bushel, 
without casks. Until a permanent demand is created little can be done, and the cost of transpor- 
tation is yet too high to admit of supplying the market, beyond the immediate neighborhood. 
Should the contemplated rail-roads come within reach of the limestone beds, the State could be 
supplied, at a price with which the Northern lime burners could not compete. 
Besides the sources of lime in the upper country, the rich marlstones of the Tertiary are weli 
