494 A. Ttjlor — Formation of Deltas. 



pauses in tlie downward movement when trees grew on the soil, and 

 vegetable matter of some thickness had time to accumulate." ^ 



In the latter part of this paper I shall suggest that the appear- 

 ances indicated in the Deltas of large rivers, of subsidence of the 

 land, may possibly be caused by a great fall in the sea-level during 

 the Grlacial Period by contraction of the sea by cold and by abstraction 

 of water for conversion into ice and snow, to be deposited on the 

 colder regions of the earth. The subsequent elevation of the sea- 

 level, and encroachment of the sea on the land, may account for the 

 shallow soundings off the Delta of the Mississippi in the Gulf of 

 Mexico. These indicate a large recent deposit there, and this may 

 have been formed during the fall in the sea-level, and then have 

 been submerged by the restoration of the sea-level to its original 

 point near the close of the Glacial Period. 



Delta of the Ganges. — From the description of Lieut. E. 

 Baird Smith, p. 4, Proceedings Geological Society, 1846, we learn 

 that between the 382 feet and 423 feet level below Calcutta in 

 the Delta was found gravel with bones of lizard and turtles asso- 

 ciated with large rolled pebbles of quartz, felspar, limestone, and 

 indurated clay. 



At the 380 feet level there occurred two feet of blue calcareous 

 clay, with many fragments of shells. At 382 feet this was succeeded 

 by a layer of dark clay filled with decayed wood, ferruginous sands, 

 and thin beds of clay from 208 feet to 380 feet From 183 feet to 

 308 feet, indurated ferruginous clay. At 175 feet a coarse friable 

 quartzose conglomerate occurs, composed of pebbles of different sizes 

 cemented together by clay. From 130 feet to 150 feet argillaceous 

 marl ; from 75 feet to 120 feet, variegated clay. At %5 feet to 

 75 feet, green siliceous clay. At 55 feet to 65 feet, clay. At 30 feet 

 to 50 feet, large portions of peat with decaying fragments of trees 

 were found. These were identified with existing species still living 

 on the spot. The clay was met with at ten feet from the surface. 

 If we apply the hypothesis of a fall in the sea-level, we have a vera 

 causa for producing a state of physical circumstances under which 

 pebbles could be transported from the high land in the interior of 

 India to an immense distance. During an average denudation of 

 100 feet over a large district, some points of land may have been 

 reduced 1,000 feet in height. If some of the mountains were 1,000 

 feet higher, and the sea 600 feet lower, we should have an ancient 

 Ganges river of immense carrying power and dimensions, such as 

 might bring down large pebbles and boulders, where now the 

 present Ganges can only bring down mud.^ 



Between Futhguhr, near Hurdwar (428 feet high), and the sea the 

 distance is 1,219 miles. Testing this section by a parabolic curve, 

 the deviation is five feet at Cawnpoor, 



' The author suggested the Delta being marine in the Phil. Mag. p. 272, and also 

 the probability of the rainfall and denudation being many times greater than at 

 present. Phil. Mag. 1853. 



"^ Mr. T. Login, Quart. Journ., vol. xxviii., has added some valuable information 

 as to the Ganges deposits. 



