DECCAN TRAP. 
150 
, CHAPTER III. 
THE DECCAN TRAP. 
Traversinff the soutlicrniiiost plateau is a series of rouf^hly 
parallel easterly to north-easterly dykes of dolerite, mostly confiii(;d 
to the Talchirs but also apj)earing in the 
Dulciitu c]> es. Barakars. These dykes, judging from their 
mineralogical characteristics, are of Deccan Trap age. They 
consist principally of augitc, plagioclase and magnetite with in- 
terstitial, partially devitrified and altered, glass. Some of them 
are free from olivine, whilst others contain it in abundance. 
They are usually non-porphyritic, but the Paradol dyke and the 
Jhiniar N. dyke, with its probable continuation, the Bhukbhuki 
dyke, contain abundant felspar phenocrysts. 
Immediately to the north of the Kurasia coalfield and 
^ J partly overlying it, the map shows a mass 
of Deccan Trap lava of very irregular shape. 
This is not composed of superficial flows of basalt or compara- 
tively fine-grained dolerite, as might at first be anticipated, but 
consists of a large intrusive sill of dolerite, coarsely crystaUine in the 
centre and more finely crystalline in its upper and lower portions, 
with the actual margins basaltic for 1 to 3 feet. This sill stretches 
in a general E. N. E. direction for 25 miles within the limits 
of Korea State, extending 13 miles further in the same direction 
into Sarguja, judging from the map attached to Hughes' memoir. 
Judging also from this map it is probable that a large number 
of the Deccan Trap outliers shown in the Sohagpur field in Rewah 
State are portions of this same dolerite sill. Its thickness is very 
variable, the smallest measurement being about 80 feet at a point 
about Ij miles north of Nagar (eastern village) ; the maximum 
thickness measured was on the hill 2,847^ west of Kurasia, where 
an approximate vertical thickness of 350 to 400 feet was measured. 
The summit dolerite being of the most coarsely crystalline type 
represents, possibly, the middle of the flow, in which case the 
sill may have had an approximate thickness of 700 to 800 feet 
at this point. Judging from the few points at which this sill was 
visited, it has a general N. N. W. dip ; at one point this dip 
could be definitely measured, namely near Nagar, where it is 22° 
