1838',] 



of the Indian Coal Fields, 



67 



Muflong. Serarim. China, 

 h a i _ „ a 



Assam. 



k L. Level of the Fossil Beach. 

 \ K 



Present Sea. 



The section of the Kdsya mountains here represented is not ideal, 

 although the horizontal distances are contracted for convenience. 



With regard to the tertiary beach L, it is a settled point in such 

 cases that it is the land and not the sea that has undergone an alteration 

 of level. The difference between the fossil beach and the present sea, is 

 consequently the quantity which these mountains have increased in 

 height since the tertiary period, indicated by the character of the shells 

 of which the fossil beach is constituted, thus accounting at once for the 

 principal difference of level between the coal at Chirra and that of 

 Burdwan on the opposite side of the delta. The bursting of a sub- 

 marine volcano between the points B, /i, from beneath a secondary 

 basin A, composed of the coal measures, would necessarily if on a scale 

 of sufficient magnitude uplift the intermediate portion of the latter, 

 separating the strata I, I, I, I, which were continuous before the elevatory 

 movements commenced. This will also account for the presence of coal 

 at the base, as well as on the summit of the mountain at Chirra*. The 

 great mass of igneous rocks e, e, e, e> which appear to have been chiefly 

 instrumental in effecting the upheavement of the coal measures, is sienite ; 

 but at i, situated on the southern side of the Bogapany river, greenstone 



* The existence of a sub-marine basin of a depth which according to these views 

 must have been equal to the entire height of the mountains, may appear to be 

 incompatible with the depth to be assigned to the sea which would appear to 

 have covered Bengal during the tertiary period. The existence of an unfathom- 

 able abyss called the swatch of no ground, close to the mouths of the Ganges, 

 and surrounded by shoal water where the deposit of silt might be supposed 

 rapidly to remove such a remarkable feature, leaves little difficulty iti conceiving 

 the great depth to which marine valleys may descend. The swatch is about 5 

 miles east of Lacont's Channel : it is fifty miles long, and thirty broad, and 

 within a mile or two of sands which are left bare at low water ; 130 fathoms of 

 line have been tried without effect, and this, within so inconsiderable a distance 

 from the northern side of the swatch, where soundings indicate only 7 fathoms, 

 as to leave little doubt of this sub-marine valley presenting as precipitous 

 declivities as we are in the habit of witnessing from the loftiest table-lands. For 

 the soundings of this basin see Horsbvrgh's Map of the Bay of Bengal. 

 K 2 



