GENERAL GEOLOGICAL NOTES. 35 



being Tipam, but tbe carbonaceous seams at the base, and the abundance 

 of silicified wood which I subsequently observed washed out of them from 

 the Chingan ridge, near the head waters of the Tiru, leave, I think, no 

 room for doubt. They overhe the coal-measures, which therefore cannot 

 be inverted, and the northern boundary of which must therefore be a 

 fault. The occmTence of Tipam beds in force south of the measures 

 shows that the northern boundary is not an original limit of deposition 

 against a pre-existing escarpment. 



The non-inversion of the coal-measures necessitates another fault 

 between them and the Disang group in the Saffrai Valley, as well as 

 between the latter and the Tipam beds north of Nangta. The same 

 reasons also lead us to conclude that both the northern and southern 

 boundaries of the coal-measures in the Janji Valley are faulted ones. 



In the Disai we have the measures flanked by Tipam beds on both 

 sides. The fault along the northern boundary is very probably the con- 

 tinuation of the main fault to the eastward, but as the intervening 

 ground, between the Disai and Janji, has not been examined, the point 

 is not beyond doubt. 



In the Makum field I observed some massive sandstones, with 

 greenish-grey clunch, of a very Tipam-like appearance, in the branch 

 of the Namdang which comes from Tuplong, and Mr. MedHcott found 

 similar beds south of the coal rocks, and apparently (according to the dips) 

 overlying them, in the Makum nadi. It would appear, therefore, that the 

 Dikhu valley structure is repeated in this part of the Makum field. The 

 main fault in all probability passes close to the base of the hills both here 

 and further east, in the Namchik field. Sub-Himalayan beds with 

 southern dip were found by Mr. Medlicott just north of the coal rock * 

 in the latter area. 



It vdll be seen, then, that according to the above interpretation, the 

 Makum, Nazira, Janji, and probably the Disai, coal-measureSj are in the 

 same line of up-throw along the southern side of the main fault, while the 

 same strata in the Jaipur field are in a different and outer line of upheaval. 



( 303 ) 



