88 mallet: geology of darjiling and western duars. 



of Baxa. The latter locality is, however, less favorably situated, as it 

 is some miles from the Raidak, which is a smaller stream than the Tursa. 

 "When the Northern Bengal Railway is complete, the lime could also be 

 burned at the western end of the range, carted to Jalpigori, and then 

 taken by rail either to the foot of the hills at Sukna, or down country. 

 By one or other of these routes it might compete with the Sylhet lime 

 from Chatak over a considerable part of Lower Bengal, if not in Calcutta 

 itself. 



Tufa, derived probably from calcareous Tertiary beds, has been 

 worked in a ravine off the Dema naddi for the supply of Baxa with 

 lime. The deposit has recently, however, been buried by a landslip. 



The tufa deposits in the Darjiling district, which are derived, 



Tufa in Darjiling dis- not from lar £ e masses of limestone, but from 

 trick rocks generally containing only a small percentage 



of calcareous matter, are on a much smaller scale than those in the 

 Duars. It is from them, however, or from similar deposits in Sikkim 

 that the lime used in the district is procured. Tufaceous masses seem 

 to be more common along the Tertiary- Damuda boundary than else- 

 where, probably on account of the issue of springs there. 



The following list includes all the localities with which I am ac- 

 quainted : — 



1. West of Pankabari, in a watercourse 500 or 600 feet above the Balasan, 

 formerly worked, but now exhausted. 



2. In the neighbourhood of the cart road, tufa is found in several of the water- 

 courses a few miles from the plains ; generally it does not exceed a few inches in 

 thickness, covering the rocks in the beds of the nallas and giving them a rounded 

 appearance as if all solid tufa.* Sometimes there are thicker accumulations. 

 The bed of one steep watercourse I ascended was lined with it for 30 or 40 yards, 

 the tufa hanging down here and there in stalactites. It is derived in this neighbour- 

 hood from Tertiary calcareous clunch, and has been worked in several places. 



* It is generally very difficult to estimate the thickness of a tufa deposit unless a 

 section is exposed by quarrying or natural fracture. 



f 88 ) 



