PHYSICAL GEOGRAPHY. 17 



Rainfall. — The average annual rainfall for the past ten years at the 

 stations nearest to the two salt-bearing tracts has been as follows : — * 



Frontier. 

 Bannu ... ... 11'26 inches. 



Kohat ... ... 17*12 inches. 



Average ... 14*19 inches. 



Salt Range. 

 Shahpur ... 1555 inches. 



Jhilam ... 24'24 inches. 



Average ... 19'895 inches. 



(The returns at Rawal Pindi are only recorded for the past seven years, 

 giving an average of 19*58 inches). 



From these figures it will be seen that more rain falls in the Jhilam 

 and Kohat neighbourhoods than in the others, but if Bannu and Shahpur 

 be taken as the two nearest stations, respectively, to these different salt 

 regions, there appears to be an excess in the Cis- Indus rainfall of about* 

 three inches yearly, which may have some influence in concealing or 

 removing the salt there more than in this region. 



Meteoric denudation leaves marked traces upon some of the rocks 

 of this district, particularly those of chemical origin, — the limestones, 

 gypsum and salt ; the action of the salt-charged water from the hills upon 

 the soft sandstone generally occupying outer or lower situations is also 

 powerful. Many of the saline streams cut flat rocky bottoms from the 

 beds, no matter in what position their stratification rests, and the stone 

 at the sides of these, liable to alternate saturation and drying, rapidly 

 disintegrates, crumbling to the touch. 



The registers of rainfall as given do not show whether there may 

 be a difference as to its periodic occurrence in the two places. The season 

 during which, the country was examined was one of exceptional cold 

 and wet, rain having fallen sometimes twice in each month. Before this 

 there was a long period without rain, and the powdery weathered portion 

 of the softer rocks seemed only waiting to be washed away, while the 

 whole country exhibited quantities of the white efflorescing salts,f some- 



* From data supplied by the Deputy Commissioner of the District. 



f Chiefly composed of sulphate of soda with a little common salt and a trace of carbo- 

 nate of soda (Dr. Fleming's 1st Report, Salt Range, J, A. S., Bengal, November, 1848, 

 p. 525). Sulphate of soda, sulphate of lime, chloride of sodium, and carbonate of soda 

 (Dr. A. Verchere, J. A. S., Beugal, 1867, p. 40). 



c ( 121 ) 



