324 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



mica-schist. The beds dip away at a sUght angle from the ravine, 

 the trough of which is filled up with volcanic tuff and ash. The 

 stream flows onwards to Bitlis through this soft and yielding rock, 

 which in the descent becomes dark-coloured and columnar, presenting 

 exactly the appearance of basalt. At one place, where it is quarried 

 for building-stone, it overlaps the edges of the mica-schist. On the 

 west of the ravine before approaching Bitlis, it alternates with, and 

 is overlaid by, an open-structured calcareous travertin. The houses 

 of the town, as well as the rock on which the old Castle of the Begs 

 of Bitlis is built, are of the grey volcanic tuff. 



Below the town the tuff gradually thins out, and afterwards only 

 occurs in patches down the valley. Two miles from Bitlis there is 

 a cold acidulated saline spring, very agreeable to the taste, and much 

 resembling Sedlitz Water. In rising from the bottom, the water 

 effervesces. There is no calcareous deposition from the spring at 

 present ; but a few feet below there is a bed of travertin which it 

 has formerly produced ; and a considerable thickness of an older 

 travertin rock here spreads along the bottom of the valley for the 

 distance of a mile. 



The channel soon becomes narrower, and is confined between lofty 

 ranges of micaceous slate, much contorted, and overlaid (I think, 

 conformably) by blue compact limestone ; both rocks dipping from the 

 ravine. This order generallv prevails to Shahtek, ten miles below 

 Bitlis. 



In some localities eruptions of basalt have broken through and 

 overspread the slates ; this is particularly observable near an old 

 caravanserai at the sixth mile. Large deposits of travertin also occur; 

 and at one place there is a very awkward descent passing through 

 a cutting made in this rock and extending to the stream in the 

 channel below. 



Further down the valley the igneous rocks are left behind, and 

 the blue limestone appears to the almost entire exclusion of other 

 deposits, and rises into lofty ranges. On leaving the Bitlis Chai, 

 this rock is crossed at Chelifteh Pass. At Werkhantz, on the S.W. 

 of this Pass, we meet with Alveolina, which proves this limestone to 

 belong to the Nummulitic Series. The descending valley or irregular 

 basin of the Kesser Sii is a mass of contorted, soft, unfossiliferous 

 gypsiferous marls and sands, resting on the skirts of blue limestone 

 mountains. 



Near Sert, m these marls, is an extensive deposit of massive pure 

 white alabaster. 



From Sert the road follows the course of the Sert Sii to the 

 Tigris, skirting the N.W. base of the inaccessible Bohtan limestone 

 mountains ; it then continues southwards along the banks of the 

 Tigris to near Jezireh-ibn-Omar, and afterwards trends away to the 

 S.W. The limestone is unfossiliferous, but undoubtedly of the 

 nummulitic age ; and, being removed from the immediate influence 

 of the igneous rocks, it assumes its wonted aspect, — being of a rich 

 cream-colour, compact, and crystalline, as at Kirrind and elsewhere 

 on the west of the igneous chain. 



