TERTIARIES. J5 



overlie the gneissose rocks. The above outcrop is the one solitary point 

 at which the Assam gneiss has been observed at the foot of the hills 

 between Nepal and the Goalpara district. 



Chapter V. — Tertiaries. 



The Tertiaries fringe the older rocks continuously from close to the 



Mechi eastward nearly as far as Dalingkot. They 

 Lithology. . 



are made up mainly of soft massive sandstones and 



clunchy beds. The most prominent variety of sandstone is a rather 

 soft, highly felspathic and slightly micaceous, white rock of medium 

 fineness, with black specks ; a pepper and salt-coloured rock. There are' 

 also light buff-coloured sandstones varying in texture from rather coarse 

 to rather finegrained, and passing into fine earthy beds. Well- 

 rounded pebbles, mostly of white quartz, but sometimes of gneiss and 

 schists, are very commonly scattered through the sandstones. Near 

 the bottom of the series they generally contain merely a stray pebble 

 here and there, but higher up, the pebbles increase in number, and 

 towards the top, layers and bands of conglomeratic sandstones are 

 frequent. The pebbles are generally under 2 or 3 inches diameter 

 and never approach in size to boulders. The sandstones are usually 

 thick and often very massively-bedded, and false-bedding is common. 

 They sometimes contain rounded concretionary masses of clunch which 

 have much the appearance of rolled pieces of foreign rock. The clunchy 

 beds are grey, greenish-grey or greenish, often micaceous and generally 

 somewhat calcareous. Usually the calcareous matter is equally diffused 

 through the rock, but sometimes it is aggregated in nodules resembling 

 potatoes in form . and size. In a few instances there are layers of 

 impure light grey limestone mixed up with the clunchy beds. The 

 latter also become bedded in places and pass into grey, slightly calcareous 

 shale. There are also dark grey shales not unlike unaltered Damuda. 

 The above varieties are generally mixed up in frequent alternations, but 



( 45 ) 



