1887.] Structure of Rocks from the Caucasus. 319 



From the north it appears to have a sharp conical summit, but it is 

 really wedge-shaped. Further westwards the ridge falls continuously, 

 a few rocky peaks protruding from it, to a well-marked snow coL 

 The drainage from the whole of this vast wall, from Koschtan-Tau to 

 the col inclusive, collects in a basin, and flows northwards as the 

 Bezingi glacier. The glacier is remarkably level and free from 

 ice-falls, and appears to start almost direct from the foot of the 

 wall, with but little sloping neve. Its course is soon narrowed to a 

 channel of some 1200 yards wide by spurs from the high ridges 

 running northwards on either side.- On the west the ridge does not 

 attain any great elevation, but on the east the glacier is bounded by a 

 group of mountains culminating in the great rock- mass of Guluku. 

 This group is completely separated from the Koschtan-Tau chain by 

 the glacier basin above mentioned.. Guluku itself is granitic in 

 character, but the lower and surrounding peaks and ridges are 

 schistose and shaly, in parts exactly like the Ober- and Unter- 

 Rothhorn on the north side of the Findelen glacier,* The upper 

 rocks of Guluku are grey in colour and look very* like granite from 

 some distance below; then comes a belt of whiter rocks (A), and 

 below that a well-marked red belt (B) ; both these belts are con- 

 tinuous and nearly horizontal for a long way roundithe southern side 

 of the peak. Below the red belt the rocks are darker and more 

 mixed (C, D, and E). On the moraine on the east side of the Urban 

 glacier, under Guluku, vast masses of granite had fallen, many of the 

 blocks recently. It is fine grained, and of grey colour (F)." 



(1.) Tau Tetnuld. — Specimen from the highest rocks about 100 

 feet below the actual summit, which was covered with snow. Mr. 

 Donkin states that the rock traversed in the asceiiti appeared to be 

 exactly of the same character. This is a flat fragment of a brownish, 

 rather fissile, but strong, mica schist, about ^ inch thick and nearly 

 2 inches broad and long. The broad surfaces are spangled with 

 small flakes of a silvery mica, and appear to be those of a " cleavage 

 foliation." Examined microscopically, the chief constitutents are 

 quartz and mica, besides which an iron oxide occurs, frequently in 

 small granules and rods, and more rarely in larger grains. The 

 quartz and mica have a general elongated lenticular arrangement 

 parallel with the broader surfaces of the fragment, and cracks 

 traverse the slide in the same direction. The quartz on applying the 

 polarising apparatus is broken up into a mosaic of different sized 

 grains united by diverse tinted margins, so that we are evidently 

 dealing in each case with one or more grains which have been crushed 

 up and re-cemented. Cavities are sometimes rather numerous, and 



* Near Zermatt in the Pennine Alps. These schists are referred to the upper- 

 most group (Graue kalkhaltige Schiefer) in the crystalline series of the Alps. 



