191^.] STEVENSON— THE FORMATION OF COAL BEDS. 537 



the plains ; the thick sandstones and sandy clays of the Tertiary 

 are, in form and composition, similar to the actual deposits of the 

 great rivers. The vast extent of the alluvial fans is illustrated by 

 one example : 



" In the range between the Jumna and the Ganges, clays are very sub- 

 ordinate and the conglomerates are formed of the very hardest quartzite 

 pebbles, just like the shingle now found in the great mountain torrents. 

 This portion of the range is, in fact, an ancient diluvial fan of the rivers 

 Tons, Jumna and Ganges. The Jumna, after its confluence with the Tons, 

 now flows very obliquely across the dun and passes through the outer range 

 far to the west of the point where it leaves the high mountains, having had 

 to double around the immense accumulation of hard materials it had form- 

 erly laid down in front of that gorge." 



The Indus is forming alluvial plains in several parts of its 

 valley within Ladak. Medlicott asserts that there is no difficulty 

 in distinguishing lake from alluvial deposits. The former are fine 

 laminated and horizontal ; but the latter are irregular, coarse and 

 may or may not be horizontal. 



The same author,^^^ in a later publication, remarks that the whole 

 plain seems to be covered deeply with alluvial deposits, for even 

 at Ambala, in the upper Indus region, a boring has shown alterna- 

 tions of sand, clay and gravel with some calcareous clay. The sands 

 are one to 41 feet thick; the clays, 3 to 40 feet; but the calcareous 

 beds are thin, none exceeding 2 feet. On the Jumna, within the 

 Gangetic area and at about the same distance from the Siwalik or 

 sub-Himalayan range, large bowlders were found at 40 feet, whereas 

 the largest fragment at Ambala is only five by two and a half inches 

 and pebbles of moderate size are not of frequent occurrence. It 

 is important to observe that no organic material has been found in 

 the deposits on either side of the divide. Borings and excavations 

 in all portions of the plain find the same alternation of sands and 

 clays. The " technical " head of the Ganges delta, as it now exists, 

 is where the Hoogly is set oiT, at 170 miles above Calcutta, which 

 is 70 miles from the sea; the nearest edge of the recent alluvial 

 plain is 80 miles west from that city — an immense area of level 

 strata. The submerged portion extends far into the sea and its 



"^H. B. Medlicott, Rec. Geol. Surv. of India, Vol. XIV., i88r, pp. 220, 

 224, 225, 232, 234. 



