42 
SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
The foregoing calculations for 397e and 397a (L and M) show at the same time the 
general dolomitic character of the carbonate, as appears from the following table, 
wherein the percentages of carbonates are given as calculated on the above-predicated 
assumptions: 
397e (L). 
Molecu- 
lar ratio. 
397a (R). 
Molecu- 
lar ratio. 
397a (Q). 
Molecu- 
lar ratio. 
397a (M). 
Molecu- 
lar ratio. 
CaC0 3 
8.95 
6.93 
.48 
1.03 
} 1.00 
7.93 
5.36 
.57 
1.15 
J 1.00 
7.11 
4.77 
.47 
1.16 
J 1.00 
6.14 
4.22 
.38 
1.15 
Mj?CO 
1 
M11CO3 
[ 1.00 
Total 
16.38 
13.86 
12.35 
10.74 
If, as is quite probable, a small fraction of the CaO should be charged to the sili- 
cates, the true dolomitic ratio would be more closely approached. It is of no conse- 
quence for the above calculations that an undeterminable portion of FeC0 3 should 
appear as MgC0 3 . The ratios are not thereby affected. 
ECONOMIC GEOLOGY OF SLATE. 
DIFFICULTIES IN SLATE QUARRYING. 
• 
The difficulties in slate quarrying are many. Assuming that the commercial value 
and the grade of fissility of the slate itself have been fully determined by scientific 
and practical tests, the opening of a quarry offers serious problems. These concern 
the thickness of the deposit and of the weathered "top," the character of the joint- 
ing, the presence of faults, shear-zones, and dikes. There are also the practical 
matters of drainage, of the location of dumps, of transportation facilities, and of fuel. 
The cost of slate at some quarries is increased by the necessity of removing the 
dumps of former workings, which, for lack of capital or of good judgment, were* 
placed on good slate. Sometimes the only way to remove these old dumps is to 
throw them into the quarry on one side and hoist them up at the other. In places 
where the beds are steeply inclined or vertical as the quarry deepens one of the 
walls falls in and the removal of this material entails great expense. The occasional 
employment of a consulting engineer would obviate mechanical accidents of this 
nature by the mathematical determination of the points at which supporting walls 
should be left. There are also uncertainties of a stratigraphic character which the 
use of the core drill would eliminate from many a slate-quarrying venture. 
The percentage of waste is generally high in slate quarrying. Watrin (see Bibli- 
ography, p. 145) , referring to the Ardennes region, gives the total waste at from 70 to 
75 per cent in weight, of which 20 to 25 occur in the quarry and 50 in splitting. 
Merrill estimates the waste in the Peach Bottom region as 88 per cent. In the Maine 
quarries it is also large, owing to the frequent interbedding of the slate with quartzite. 
BEDDING AND CLEAVAGE— HOW DISTINGUISHED. 
Wherever the slates are traversed by "ribbons," or marked changes in coloi 
occur and persist through a thickness of several feet, or wherever strips of quartzite 
or limestone occur at intervals and continue longitudinally for several hundred feet 
quarrymen of any experience know that they have to do with beds, and that th< 
quality of the slate of any one bed may be expected to continue along that bed 
unless some change should occur in the character of the cleavage. The quality o 
the slate is primarily dependent upon the character of the sediment. This change 
less frequently in a horizontal than in a vertical direction. The changes in the char 
acter of the materials brought into the sea and deposited at one time throughout : I 
