80 mallet: coal-fields of the naga hills. 



ai-e also met with lower down, but less abundantly. There, the general 

 silicification seems to have been more complete. 



The thickness of the group is very great. From the lowest beds 



overlying the coal-measures north of Jaipur, to 

 Thickness. _ ^ ^ 



the base of the Dihing conglomerates near the 



mouth of the Namsang nadi, is about four miles in a line perpendicular 



to the strike. The average dip, of probably 20 to 25 degrees, would 



therefore indicate in this section an accumulation of some seven to nine 



thousand feet. 



Biking group. 



At the bend of the Dihing, three-quarters of a mile below the mouth 

 of the Namsang, the massive, false-bedded Tipam sandstones include 

 short, irregular bands of coal-conglomerate and pieces of semi-carbonised 

 wood. Somewhat higher stratigraphically, at the mouth of the Nam- 

 sang, such layers of conglomerate are well seen, and here there 

 is much wood also. The pebbles are, naturally, of the harder kinds 

 of coal, and are mixed with a few others of sandstone and small 

 ones of quartz and hornstone. Some layers are made up almost entirely 

 of coal, but most of the rock contains a good deal of arenaceous matrix, 

 and is friable and rusty. The wood is mainly in a semi-carbonised con- 

 dition only. It has a brown color, and more or less retains the toughness 

 of wood. In part, however, especially in the outer portions of the 

 stems, it is black and brittle. Other parts, again, chiefly the central 

 ones, are more or less completely sihcified (although still retaining their 

 dark carbonaceous color) so as to strike fire with the hammer. Both 

 the silicious and carbonaceous portions frequently have many of the 

 vessels filled with pyrites. Large pieces of such wood are very common 

 in these beds, one log I measured being a foot in diameter and 10 feet 

 long. 



The coal conglomerate extends along the south-eastern border of the 

 Tipam range as far as the Janglu nadi. The continuation of the section 

 is well seen in the reach of the Dihing above the Nara Latta nalla, where 



( 298 ) 



