52 mallet: geology of darjiling and western duars. 



strike, and still more in thickness. The sections are seldom sufficiently 

 good to trace the seams by means of the associated beds. Thus the 

 same seams almost certainly out-crop more than once on the cart-road, 

 and the 6 -feet Tindharia seam may be the same as the 11-feet one. 



I have included all out-crops of 2 feet and upwards in the list, 

 Rapid variations in nofc on the supposition that a 2-feet seam of coal 



thicknesses of seams. would pay to WQvkj ^ ag j haye previougly 



explained, the seams vary greatly in thickness within a few yards. Thus, 

 one of those in the Chirankhola is 8 feet on one side of the stream 

 and only 2 on the other, and another on the cart road varies from 1 

 foot to 3 feet 6 inches in the short distance along which the out-crop 

 is visible. A thickness of 2 feet at the out-crop may be the minimum 

 thickness of the seam. 



There can be no question that these rapid variations are due mainly, 

 or almost entirely, to the crushing which the rocks have undergone ; but to 

 some extent they may be caused by variations in the thickness of the bed 

 as it was originally formed. How much should be attributed to the latter 

 cause is a most important element in the question of working the coal, 

 and it was partly to gain information on this point that I recommended 

 horizontal trial drifts to be driven into a couple of the more promising 

 seams, namely, the 11-feet seam in the Tindharia ravine and the 7-feet one 

 in the Chirankhola. Mr. Tyndall, Executive Engineer of the Darjiling and 

 Jalpigori Divisions, under whom the work was put, was unable to break 

 ground at the latter during the rains. The drift into the Tindharia 

 seam had been driven 40 feet in from the out-crop, at the commence- 

 ment of the rains, and the seam was reduced to 6 feet. It is, how- 

 ever, very probable that it again increases in thickness further in; 

 and with a view to ascertaining the mean thickness of the bed here, and 

 whether it maintains that thickness for some distance, or dies out partially 

 or altogether, as well as to gain information as to the constancy or otherwise 

 of the dip and strike, and whether the seam has been faulted or not, I 



( 52 ) 



