PETROLOGY. 29 



able, notwithstanding the large supply of charcoal always available 

 from the surrounding forests. 



A very conspicuous difference between the sand-rock and the 

 Nahan sandstone is that the latter is traversed by numerous joints, 

 parallel and at right angles to the bedding planes. Thus, the rock 

 splits with readiness into blocks and slabs. The jointing is more 

 marked in the lowermost Nahans, and less in the uppermost. 



The thickness of the Nahan sandstone canno be definitely estim- 

 ated ; because, in the first place, the base is nowhere seen, and, in the 

 second place, the strata are folded in the typical zones with an un- 

 known amount of fold-faulting. In the Pel£ni N. the middle Nahan 

 sandstone zone is 4,950 feet thick, from the base of the sand-rock 

 down to the anticlinal north of the Nahan-Siwalik boundary. The 

 middle band in the Kotri river gives a visible thickness of 6,270 feet. 

 Thus, we can only say that at least it is as thick as the latter value. 

 Regarding the whole of the Siwalik series, from the visible base 

 Whole of Siwalik °f tne Nahans up to the top of the Siwalik con- 

 senes# glomerate, one is impressed by the aspect of 



a great conformable and connected formation, but one which must 

 have taken a long epoch of time for its deposition. There are three 

 standards by which one is able to infer that that epoch was of great 

 duration. In the first place, the immense thickness of the deposits 

 (which average at least 16,500 feet, or over three miles) render it im- 

 possible, except on some cataclysmic theory, that they could have 

 been accumulated in a brief interval. Secondly, the difference in the 

 consolidation of the rocks forming the lowest and highest beds in 

 question (which difference is well seen in the Nahan and middle 

 Siwalik stages), shows a great aging of the lowest members. Third- 

 ly, the relative differences in the disturbance which has affected the 

 lower and higher parts of the series, and which we shall see later 

 on resulting in the apparent anomaly of marked unconformability 

 between the uppermost and the lowermost beds with continuous con- 

 formability between consecutive stages, point in the same direction 

 and argue a long epoch of time. 



( 87 ) 



