250 ANNUAL REPORT 
a moisture content of fiom 50 to 70 per cent.; 10 cubic feet may be safely 
taken as the average. In prospecting a marl deposit, it 1s extremely im- 
portant to make numerous borings in order to calculate the available marl. 
Owing to the extreme variations which this material is lable to show, it 
is quite deceptive, and often the variation is far greater than appears on 
superficial examination. Neglect to look this over carefully has neces- 
sitated the closing down of more than one marl plant. In Michigan the 
mar] area controlled by a single cement plant varies from 260 to 2,000 
“acres. 
Steam Shovel. —The steam shovel cannot be employed, as a rule, 
for winning limestone, though the writer has seen one most powerful ma- 
chine at work at the Edison Portland Cement Company. In this case a 
cement rock is being worked by blasting, the machine taking up the 
loosened material. Calcareous material, of a soft mature, like 
dry marls, chalk or soft limestones can be worked very economically by 
means of the steam shovel, and the cost will not be much more than 5 
cents per cubic yard. 7 
Mining—What has been said in regard to clays applies also here, 
excepting that limestones would be less difficult to mine, owing, as a 
rule, to the better roof available and the more stable character of the 
pillars. But the cost, though not as great as for clay, would not be very 
much less, probably not less than 40 cents per ton. 
HAULAGE OF RAW MATERIALS TO WORKS, 
There are available four means of conveying the raw materials to the 
works, which are: 
| Calolle 
I. Tramways..< Electric locomotive 
Steain locomotive. 
2. Aerial cableways. 
3. Transportation by water. 
4. Pumping. 
The method of haulage to be adopted depends on the distance to be 
covered, the quantity to be conveyed and the topographical conditions. 
Tramways.—Cable tramways are suited only for short distances and 
are especially useful in dealing with heavy grades. For larger capacities 
the rope should be endless so as to keep cars going steadily in one direc- 
tion. Where the grade is sufficient in the right direction, a gravity sys- 
tem can be installed, the loaded cars pulling up the empty ones. It 1s 
unnecessary to go into details of construction of such plants, since these 
have been thoroughly worked out for mining work and such a discussion 
would be beyond the scope of this report. The distance should not exceed 
about 1,500 feet. Electric and steam propelled locomotives are adapted 
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