142 RANIGANJ COAL FIELD. [CHAP. VIII. 



Asansol dak bungalow, is about 120 feet broad, and it has throughout 



a general direction of South 20° — 25° East. No other dyke, within the 



area of the field, attains equal dimensions, although a few nearly parallel 



with it, are of considerable breadth (30 or 40 feet), and can be traced 



for many miles. By very far the largest portion, however, do not 



exceed 3 feet across, but even these may, in many instances, be seen to 



extend for 5 or 6 miles. 



The trap forming the various dykes differs greatly in mineral charac- 



Mineral character of ter. It is generally more or less decomposed, and 



dy frequently contains a whitish micaceous mineral, 



somewhat resembling Margarodite, in little rounded masses. In many 



instances it contains black mica. But these distinctions do not certainly 



prove difference of age, for two or three varieties are frequently found 



in the same dyke, in different portions of its course. Small pieces of 



gneiss and granite, brought up evidently from the metamorphic rocks, 



which must be in some places 10,000 or 12,000 feet below the surface, 



abound in some of the dykes, and occasionally in very small ones. 



Among the great mass of the dykes in the beds of the Raniganj 



field, above the Lower Damudas, no reliable dis- 

 Distinction as to age. 



tinction can be made as regards age. There are, 



however, some appearances, which induce the belief that the traps 



running in general East and West, between Etiapora, Samdi, and the 



Barakar, those North of Chtiralia and Madanpur, and others in the 



Lower Damudas, are older than those spread over the remainder of the 



field. Their distinctive peculiarities will be described presently. 



There seems, among the greater number of the remaining dykes, to be 



a prevalent direction, averaging North-east and South-west, a far 



larger number striking between North and East than between North 



and West. This is doubtless due to the circumstance of the forces 



which had disturbed the district previous to the trap intrusions, having 



produced numerous cracks in this direction, which is that of a large 



