34 mallet: geology of darjiling and western duars. 



north, the inclination of the Baxas being 1 generally high ; there are of 

 course many minor rolls by which the dip is locally reversed or altered. 



The most prominent, and, economically considered, the most import- 

 ant member of the series, is a magnificent band of dolomite which is 

 traceable from the Rehti naddi to the Tursa, and again for some miles 

 east of Baxa. The rocks above and below it being comparatively soft 

 slates, &c, the dolomite rises into a boldly outlined ridge, sometimes as 

 much as 3,000 feet high. The rock is very massive as a rule, with little 

 bedding discernible, but not unfrequently it is shaly, and passes into dark- 

 grey slate. It has a saccharoid structure and light-grey color, but the 

 impure shaly parts are darker ; there is an exceptional variety that is 

 finely granular and almost pure white. Nests of more largely crystalline 

 calcite, and little drusy cavities lined by crystals of the same mineral, 

 are often profusely scattered through it. Mr. Tween's analyses of 

 specimens from the Tfti naddi, show that it contains about 60 per 

 cent, carbonate of lime to 38 carbonate of magnesia, and it is pro- 

 bably a normal dolomite (= carbonate of lime 54*35, carbonate of 

 magnesia 45*65), owing its excess of lime to the crystals of calcite 

 which are disseminated through it. These crystals represent the cal- 

 careous excess in the original matter from which the rock was formed. 



The entire thickness of the Baxa beds is uncertain, as the base 

 of them is nowhere seen. A section is visible on the right side of the 

 Pagli naddi, near the frontier, the lowest strata in which are very brittle, 

 flaggy, silicious beds, with impure calcareous layers interbanded, dipping 

 north-north-east at 30°. These are covered by a few feet of green and 

 white talc schist, and then by slaty, granular quartzite. Beyond is blank 

 for some distance, and then dipping north at 60° are light green and red 

 slates with thin calcareous layers, covered by some hundred feet of white 

 slaty quartzite or quartz schist. Large blocks of the dolomite are 

 brought down stream from the north, showing that that rock is still 

 higher in the series. 



( 34 ) 



