GENERAL GEOLOGICAL NOTES. 17 



rocks in situ do exist near the head-waters of the Saffrai, their extension 

 must be very limited. It is difficult to understand how they could be 

 brought in there only without considerable faulting. 



No crystalline debris is to be found in the Dikhu, the J^nji or 

 the Disai ; but it is abundant in the Dhansiri (including, amongst other 

 varieties, numberless pebbles of grey translucent quartzite, derived no 

 doubt from the Shillong series). Immediately west of the Dhansiri we 

 come upon the grealfc mass of metamorphic rocks which form the northern 

 portion of the Mikir, Jaintid,, Khasi and Garo Hills.* The strike of the 

 metamorphic-sedimentary boundary, if produced into upper Assam, below 

 the alluvium, would, on account of the trend of the hills east of the 

 Dhansiri, pass to the north of their base. Hence the absence of the 

 former^rocks along the skirts of these hills is not surprising. 



Major Godwin-Austen mentions " contorted clay shales and schists^' 

 as appearing from beneath the tertiary rocks close to Japvo, a peak of 

 the Barail range to the south-east of Samaguting, nearly 10,000 feet high. 

 But their extension yet remains to be traced.f 



Cretaceous group. 

 The band of cretaceous rocks which overlie the metamorphic strata 

 on the southern side of the Garo- Jaintia hills, also comes to an end at the 

 Dhansiri, and no representatives of this group have hitherto been found to 

 the east of that river. The furthest point to which they have been 

 traced is the mouth of the Nambar, which joins the Dhansiri some miles 

 above Golaghat. They may exist beyond this underneath the alluvium, 

 but they do not rise to the surface along any part of the base of the hills 

 that has yet been surveyed. J 



* The difference in the rocks cut through is well shown at the junction of the Doyaug 

 and Dhansiri, the former of which brings down dark-grey, and the latter red, sand. 



t Journal, Asiatic Society Bengal, Vol. XLIV, pt, 2, p. 210. 



% A few miles west of Bor Pathar, in the Nambar, there is a bed of cretaceous coal, 

 information of which I received from Mr, Coombes. This is probably the seam from which 

 the fragments found by Mr. Brodie in 1837 were derived (p. 4). It appears to be some 

 C ( 285 ) 



