GENERAL GEOLOGICAL NOTES. 19 



high angles. These beds are seen for some distance up the river and have 

 a considerable thickness : then, north-east and east of Naogaon they 

 become interbanded with, and pass up into sandstones. The latter are grey, 

 or greenish-grey ; fine-grained and rather hard ', they are mostly thin- 

 bedded, with occasional layers of grey shale, but in some parts thick and 

 thin beds are intermixed. It is of this rock that the Naogaon ridge is 

 composed. Lower down stream, loose pebbles of sandstone of the same 

 kind, intersected by thin seams of quartz, a sixteenth or less to one or 

 two inches in thickness, are common, the quartz frequently having a 

 finely columnar structure perpendicular to the walls of the vein. I 

 have not seen such vein rock in situ, but it not improbably comes from 

 the above-mentioned strata'^. 



In the Makum field, beds very similar to those on the Disang are 

 found to the south of the coal, but the shales and sandstones are, perhaps, 

 less clearly demarcated. Between the coal-measures south of Kerimgaon, 

 and Rangkatu, these strata mainly consist of grey and brownish- grey 

 shales (sometimes clunchy), with sandstones which are generally fine- 

 grained, thin-bedded, and rather hard when unweathered. 



"West of the Disang, the grey shales are well seen in the Teok ; and 

 in the Chota Taukak a fine section is exposed, resembling that in the 

 Disang ; grey shales interbanded with more or less sandstone are succeeded 

 by tolerably hard, fine-grained sandstone, in thinnish beds with some 

 thick ones. Good sections are also found in the Saffrai itself, and in the 



* Possibly some of the gold found in the rivers flowing from the Naga hills is derived 

 from these quartz veins. The Janglu or Joglo nadi in the Tipam range, and the Disai are 

 said to have yielded the purest and best gold in former times, when washing was carried on to 

 a considerable extent in Assam (Journal, Asiatic Society, Bengal, Vol. VII, p. 626, and XXII, 

 p. 511). The upper part of the latter stream has not been examined geologically, but it is 

 very improbable that it flows through rocks older than those of the Disang group, while the 

 course of the former is almost certainly entirely over rocks of the Sub-Himalayan series. 

 Some of the gold in the Disai may be from the quartz veins, but that found in the Janglu 

 can hardly be otherwise than doubly derivative. This latter fact has also been observed 

 in the Sivaliks of the north-west Himalayas, (Vol. Ill, pt. 2, p. 179.) 



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