18 E. D. Oldham — Essays in Theoretical Geology. 



In all the sections of the sub-Himalayan beds there is a marked 

 and steady increase in coarseness of texture as we ascend the section. 

 This feature is everywhere observable in the sub-Himalayan sections, 

 and even in the Sirmur series of the Simla Hills there is a steady 

 increase in the proportion of sand to shale from the purely argilla- 

 ceous Subathu group to the chiefly arenaceous Kasaoli group. This 

 gradual upward increase in coarseness of texture on any one section 

 is an inevitable result of the gradual southwai'd extension of the hill 

 area; for by it the region of fine-grained silts is brought within 

 reach of the sand, and, finally, of the shingle deposits. But besides 

 the increase in coarseness of texture on each section, it is an indubit- 

 able fact that the texture of the coarsest beds of each group or 

 division increases with its decrease in age, and this appears to me to 

 be due to a gradual increase in the average size of the debris brought 

 down by the Himalayan streams. 



I have already shown that in Eocene times the North- West 

 Himalayas did not exist, and that in Siwalik-Pliocene times there 

 was a mountain range whose hydrography agreed with that of the 

 present day in its main features, and that, to judge by the nature of 

 the burden carried by the rivers, this range must have been com- 

 parable in elevation and extent to the present Himalayas. During 

 the Tertiary period, then, the Himalayas were in process of elevation, 

 and it is natxiral to suppose that, during the earlier part of this 

 process, the gradients of the streams and their powers of trans- 

 portation would be less than at a later period, and that, consequently, 

 no great deposits of coarse gravel could be found. This supposition 

 derives great support from the fact that throughout the great thickness 

 of the Dagshai and Kasaoli groups, and of the Murree group, not a 

 single pebble has been found, while with one very doubtful excep- 

 tion ^ no conglomerates of Nahan age are known. 



In the foregoing passages it has been tacitly assumed that elevation 

 has always been accompanied and caused by disturbance of the beds 

 elevated, and such, in the main, is the case. There are, however, 

 recent undisturbed gravels which rise, in the sub-Himalayan region, 

 to heights of 500 feet above the present river-beds and seem to 

 indicate that there has been a certain amount of elevation unaccom- 

 panied by disturbance of the horizontality of the beds elevated. So, 

 too, the fossiliferous Pleistocene deposits of Hundes have probably 

 been elevated without disturbance to some extent, though not so 

 much as was supposed by the earlier observers.^ With these sub- 

 sidiary exceptions, which do not affect the general principle, it is 

 true that, in the Himalayas, elevation has always been a result of 

 the compression and disturbance of the beds elevated. 



1 Mem. Geol. Survey India, vol. iii. part ii. p. 135. 



2 Lydekker, Rec. Geol. Survey of India, vol. siv. pp. 178-183 (1881). 



(To be continued.) 



