<56 On the difference of level [Jan. 



On the eastern side of Calcutta on the contrary, there is a depres- 

 sion, though probably of less amount, extending gradually to that portion 

 of the Sunderbunds marked 'morass,' in Arrowsmith's map, a little 

 on the west of Culna. This lowest situation perhaps of the Sunder- 

 bunds, is situated midway between the Tiperah hills on the east, and 

 those hills the continuation of which on the western side of the Hoogley, 

 contains the Burdivan coal field ; the distance across the alluvium on 

 either side being about 150 miles, making the breadth of the united 

 delta of the Ganges and Brahmaputra, at this situation 300 miles. 



If from the morass, we proceed two and a half degrees due north, 

 we find the breadth of the great delta contracted between the Garrow 

 and Rajmahl hills to 150 miles, from which situation the alluvium 

 again expands into the plains of its respective rivers, extending north- 

 west and north-east respectively, and leaving an obtuse angle formed 

 by the Sikkim and Bhotan mountains, pointing toward the great delta, 

 and forming with the Rajmahl and Xjlarroiv mountains three points of a 

 nearly equilateral triangle, which constitutes the nearest local con- 

 nexion of the three distinct systems of Indian mountains ; and at each 

 of the three situations, viz. Rajmahl, Chilmary, and the Teesa river 

 coal has been found. 



It would be hazardous to draw any conclusion from this interesting 

 fact, until we are better acquainted with the nature and relative position 

 of the strata in each locality. Should the coal of the three situations 

 prove to be the same formation, borings in that case conducted in 

 various intermediate points in Purnea and Dinagepore, might detect 

 the coal measures buried beneath this portion of the delta ; (vide a. A, 

 Fig. 1) but at present our data are too vague to justify the expense of 

 such a mode of inquiry in this quarter. It would rather seem that the 

 intervening coal measures were upheaved with those of the adjacent 

 mountains, and subsequently overthrown by the Ganges and Brahma- 

 putra, or by other causes hereafter to be considered. 



Although we have at Chirra Punji, a bed of coal raised on an 

 insulated summit 4300 feet above the level of the sea, the rocks by 

 which it is accompanied are identical in their nature with those that 

 are found bearing a similar relative position to other beds of coal of 

 the same formation, whether above or below the level of the sea. The 

 annexed figure will render these observations better understood. 



a a a a a Coal, b b Great sandstone forming the base of the coal measures. 

 ee.ee Igneous rocks, y Basaltic quartzose-rocks, reposing on the greenstone (i.) 

 i Greenstone, h Granular slaty quartz, or metamorphosed sandstone. 

 k Nummulite limestone, m Slate clay. 



h New sandstone, containing in the south side of Assam fragments of c. aland 

 fossil trees. 



