DETAILED DESCRIPTIONS OF THE RESPECTIVE COAT-EIELDS. 17 
three bands of clay aggregating^ 4 foot 3 inchoa in thickness. The 
dip varies from 42° to 65°. Tlie quality of tho coal is excellent. 
It is, however, doubtful if much of the coal lies above water level 
and could be worked without heavy pumping. 
Makum.— The Makum field is the best known of the several 
coalfields lying along the lower ranges of the hills which form 
the southern boundary of the Lakhimpur and Sibsagar districts. 
The coal-bearing rocks dip at high angles towards the axis of the 
range, and their outcrops occur as a narrow strip some 18 miles 
in length by about one mile in breadth. The coalfield is probably 
faulted on the noith, but such distui-bance is hidden by the allu- 
vial plain of the Dihing river, which flows parallel to, and about 
3 miles from the northern boundary. The most valuable seams 
occur in the east of the field between the Tirap and Namdang 
streams, a distance of about 5 miles. Throughout this ground the 
existence of a coal-seam, from 15 to 80 feet in thickness and pro- 
bably not averaging less than 50 feet, has been proved. Several 
other seams are also said to occur. The average dip of the rocks is 
about 40° and consequently the seams pass into depth at short 
distances from the outcrops. Fortunately from a mining point of 
view, the outcrops in many places are several hundred feet above 
the plains, and consequently facilities for working the coal by 
means of adit levels are afforded. 
Mallet ^ in 1875 est mated that between the Tirap and Nam- 
dang streams within a vertical depth of 400 feet from the outcrop, 
there is a minimum quantity of 18 milHon tons of coal. Sub- 
sequent working has proved the great seam to have a greater aver- 
age thickness than was apparent during the prospecting stage, and 
in 1900, Mr G. E. Harris,^ the manager of the collieries, estimated 
that over the same ground above the natural drainage of the 
Ledo and Namdang streams, there is a total quantity of 90 million 
tons of coal. 
Small quantities of coal had been mined from this field in early 
times, but extensive operations were not commenced until 1881, 
when a mining concession was obtained by the Assam Railways 
and Trading Company, who at once commenced the vigorous ex- 
ploitation of the coalfield. A metre-gauge railway, 77 miles in 
length between the Brahmaputra near Dibrugarh and the coalfield, 
1 Op. cit. 
* Trans. Manchester Geol. Soc, XXVI, p. 578. 
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