538 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i, 



deposits are approximately horizontal. The depth of water in the 

 Bay of Bengal is small, but outside of the delta area, there is a 

 deep depression known as the " Swatch of no ground." All around 

 it, soundings give a depth of 5 to lo fathoms, but in the " Swatch " 

 that increases abruptly to 300 fathoms. Fergusson,^^* cited by 

 Topley, has shown that this space is kept open by currents, which 

 may have kept it clear while the adjoining area was filling. In that 

 case, the alluvial deposit would be at least 1,800 feet thick. A bor- 

 ing at Calcutta has proved it to be not less than 481 feet. 



Lyg,]p35 relates that at no place in the delta proper or for 400 

 miles from the sea does one see any gravel, the whole plain of Bengal 

 being overspread with Himalayan mud, homogeneous but becoming 

 more sandy near the hills and occasionally containing abundance of 

 land shells. Those who sail down the river in time of flood see 

 nothing but a sheet of water in every direction, except here and 

 there where the tops of trees emerge above its level. Xo reference 

 to vegetable matter is made by Lyell or by any other observer to 

 whose work the writer had had access — though the mud is exposed 

 in river cliffs, 80 feet high near Calcutta. Lyell mentions the 

 boring at Calcutta in which peat was pierced at 50 feet. Blanford, 

 in the work already cited (p. 400), says that this peat bed is found 

 at 20 to 30 feet from the surface in all excavations around the city 

 and that it seems to extend under a large area in the surrounding 

 country, having been met with in borings even to 35 miles south- 

 east and to 81 miles east by north. Lyell states that this was con- 

 sidered to be an old soil, carrying a vegetation similar to that of 

 the present Sundurbund. Logs and branches of red-colored wood 

 occur above and below the peat, so little changed as to be identi- 

 fiable, and they were recognized as the Soondri tree, now prevalent 

 at the foot of the delta. In this Calcutta boring, clay, sand and 

 pebbles were pierced at 120 feet and another forest bed was reached 

 at 380 feet, while the boring ended in beds of pebbles, sands and 

 bowlders. The conditions throughout suggest that, before sub- 



"'W. Topley, "India." Encyc. Brit., 9th ed., Vol. XII., p. 736. 

 /"C. Lyell, "Principles of Geology." 1872, Vol. I., pp. 476, 477; "The 

 Geological Evidences of the Antiquity of Man," New York, 1871, pp. 336, 



337- 



