420 J. BARRELL RECOGNITION OF ANCIENT DELTA DEPOSITS 



almost entirely replace it. This clay, even wlieii tilted to the vertical, is 

 mulistiiiiiiiishable in hand specimens from that ot the recent ])lains deposit: 

 and no donht it was formed in a similar manner, as alluvium. The sandstone, 

 too. of this zone is exactly like the sand formini; the hanks of the jjcreat rivers, 

 but in a more or less consolidated condition. Thus it was suijcuestive. antl not 

 altogether misleadini;, to say that the Siwaliks were formed of an upraised 

 IK)rtion of the plains of India. 



"The fresh-water origin of the Siwalik formation seems almost as indisput- 

 ahle as the marine origin of the 8ubathu beds: yet. until lately (1870), it has 

 been usual to consider the Siwaliks marine. The notion was probably a relic 

 of the opinion that a water basin was an essential condition of the extensive 

 accumulation of deposits, and that a sea margin would be required lor such a 

 great spread of shingle as that of the Siwalik conglomerates. The saiiie opin- 

 ion, on the same grounds, has been extended to the plains deposits themselves. 



"The continued experience that the fossil remains in these Tertiary strata 

 are exclusively' of laud or fresh-water organisms, made this view untenable : 

 nnd in time it came to be realized that the deposits themselves bear out the 

 same opinion: the mountain torrents are now in many cases engaged in laying 

 down great banks of shingle at the margin of the plains, just like the Siwalik 

 conglomerates : and the thick sandstones and sandy clays of the Tertiary series 

 are of just the same type of form and composition as the actual deposits of 

 the great rivers. 



"Beds of this character alternate with the upper beds of the Subathu 

 group ; so it seems probable that from early Tertiary times the sea has been 

 excluded from the sub-Himalayan region, and tliat the whole of. the sub- 

 Himalayan deposits, above the Subathu group, are fresh-water and fluviatile. 

 and formed on the surface of the land. They are in fact subaerial formations, 

 like the river alluvium and bhabar deposits of the present day." 



Speaking of these formations as they occur in the Salt Range in the 

 Punjab, Wynne makes the following statements :^' 



"Everywhere from one end of the range to the other, and always on its 

 northern and eastern aspects, the uppermost rocks of the Salt Range series 

 are innumerable alternations of gray or greenish sandstones, of not great 

 hardness, with red or light-bi-ownish orange clays, more rarely with conglomer- 

 ates, but rre(|uen(ly with harder tine-graiiicd sandy beds of peculiar concre- 

 tionary pseudo-congloiueralic structure. . . . The alternating bands of 

 sandstone and clay are from seventy to a hundred and twenty feet in thickness, 

 being very frequently about a hundred feet isicli. l)ut some zones are much 

 thicker." 



It is the Middle Siwalik which especially shows the association of gray 

 or green sandstones and red clays. All parts contain the bones of mam- 

 mals and fresh-water reptiles. It is seen from this description that such 

 combinations of red clays and gray or green sandstones are features of 

 fluviatile deposition under certain intermediate climatic conditions. The 



" Memoirs of tho Geological Sm-vo.v of India, vol. xiv, 1S7S. p. 108. 



