Lieut. R. B. Smith on the Delta of the Ganges. 519 



Nov. 16, 1842. — A paper was read " On the Structure of the Delta 

 of the Ganges, exhibited by the Boring Operations in Fort William, 

 a.d. 1836-40." By Lieut. R. Baird Smith, B.E. 



Since the year 1804, a number of boring operations have been 

 conducted in the Gangetic Delta, with a view to supply the deficiency 

 of good fresh water in the vicinity of Calcutta, but, from mechanical 

 obstacles, without success. The geological results of the last of 

 these experiments, commenced in April 1836, and abandoned in 1840, 

 after being carried on to the depth of 480 feet, are detailed by Lieut. 

 Smith in this memoir. After penetrating to the depth of ten feet 

 through the artificial surface soil, a bed of blue clay, close and ad- 

 hesive in its texture, was entered. As the bore descended, the clay 

 became darker in colour, till, in from thirty to fifty feet, large por- 

 tions of peat, with decaying fragments of trees, were found. These 

 Dr. Wallich identified with the common Soondri of the Sunderbunds, 

 and the roots of some climbing tree resembling Brcedelia. The stra- 

 tum of peat and decayed wood was therefore formed from the debris 

 of forests which at a former period covered the entire surface of the 

 Delta, as the existing jungles of the Sunderbunds cover so large a 

 portion of it now. In one instance bones were found in the peat, 

 but they were unfortunately destroyed by the workmen before exa- 

 mination. Succeeding these peat-charged beds, a stratum of calca- 

 reous clay, ten feet in thickness, is found, and intermixed with it 

 are portions of the concretionary limestone, commonly known in 

 India as kankur, which Lieut. Smith regards as formed by the se- 

 gregation of the particles of calcareous matter disseminated through- 

 out the body of the clay with which it is associated, and as nearly 

 contemporaneous in -its origin with this clay. Underlying the bed 

 of calcareous clay in which the kankur first occurs, there is a thin 

 bedjof green siliceous clay, extending from sixty to sixty-five feet in 

 depth. The clay then loses its colour, and continues to a depth of 

 seventy-five feet, the lower portion of it furnishing nodules of kankur. 

 At seventy-five feet, a bed of variegated, sandy, or arenaceous clay 

 commences, and continues to the depth of 120 feet, occasionally 

 traversed by horizontal beds of kankur. Beneath this is a stratum of 

 argillaceous marl, five feet in thickness ; and succeeding it there is a 

 bed only three feet in thickness, of loose friable sandstone, the par- 

 ticles of sand being held loosely together by a clayey cement. Ar- 

 gillaceous marl, twenty feet in thickness, follows the sandstone, ter- 

 minating at the depth of 150 feet, when it passes into an arenaceous 

 clay, intermixed with water-worn nodules of hydrated oxide of iron. 

 Weathered mica slate is found attached to the clay of this bed, and 

 throughout the entire range of strata penetrated, scales of mica have 

 always been abundantly met with. At 175 feet, a coarse friable 

 quartzose conglomerate occurs, composed of pebbles of different sizes, 

 though none are very large, cemented together by clay. At 177 

 feet, this conglomerate becomes smaller grained ; and at 1 83 feet 3 



logy of North America, by Dr. Dale Owen, Mr. Lyell, Dr. Mantell, Mr. 

 Redfield and Mr. Cooper, read before the Geological Society from Nov. 2, 

 1842, to Feb. 1, 1843, have been given in the present volume, p. 180. 



