374 JRevieHS — G. 2Ierzbacher — On the Caucasus. 



opinion " rein tbeoretiscb," forgetting to remark that I carefully 

 stated this to be an hypothesis which, with one or two more, was 

 advanced as being, in my opinion, " the most probable interpretation 

 of such facts as have been ascertained." 



Herr Merzbacher collected a fair number of geological specimens, 

 which are minutely described by Dr. L. von Ammon in an appendix. 

 The latter separates them into four groups : (I) the Archtean rocka 

 of the Central Jfassif; (II) diabases and contact rocks from Gimarai- 

 Choch to Kasbek ; (III) black shales or slates,^ and sandstones ; 

 (IV) younger eruptive rocks. He also has given a note on some 

 sinter from the hot springs of Saniwa. (I) Additions have been 

 made to the detailed knowledge of the Central Massif even since 

 the publication of Mr. Freshfield's volumes, and now Dr. von Ammon 

 describes specimens collected from some of its important summits. 

 Among them is a gneiss, with two species of mica, from Dongus- 

 orun ; the rocks on the upper part of this mountain are mostly 

 granitic, and Dr. von Ammon thinks the gueissic character of this 

 specimen may be due to pressure. Next come a white granite, 

 containing, however, some scales of biotite (passing into a chloritic 

 mineral) from Uschba : a biotite granite from Sulu-kol-Baschi ; 

 granite with two micas from Tetnuld : green-speckled white granite 

 from Dschanga-tau (these three being the highest rocks on the 

 peaks) with a chlorite epidote schist and a quartzose epidote rock 

 from the last-named mountain, a rather fine-grained green- speckled 

 granite from the peak of Sugan-Tau, and a diabasic rock from 

 that of Tepli. The localities rather than their petrographical 

 character give an interest to all these. So it was with the few 

 which I examined for the late Mr. Donkin in 1887. (II) Gimarai- 

 Choch, 15,676 feet high, lies rather more than five miles to 

 the west of Kasbek. The rock of the actual peak is a diabase, 

 which has been minutely examined, but seems not to be specially 

 interesting, except that a little quartz is present ; varieties of 

 the same rock were brought from a rather lower level, on one 

 of which were some glass splashes, doubtless due to lightning ; 

 a schalstein or diabase tuff was obtained rather more than 300 feet 

 below the peak, and specimens of sedimentary rocks {JwrnscMefer 

 and schieferiger Jwrnfels), probably members of the next group, were 

 also obtained on this mountain. (Ill) Dr. von Ammon separates 

 these (sedimentary rocks) into three groups : (a) the first, dark 

 schiefer, he assigns, for reasons presently to be given, to the 

 Jurassic system ; (b) the second, also black schiefer, from the 

 Pirikitelisch range in the Eastern Caucasus and from Daghestan ; 

 (c) those from Laila. They have been carefully studied, for doubt 

 has been expressed as to their geological age. Favre claimed 

 to have identified Bytliotrepliis in some, and assigned these to 

 the Palfeozoic era. This identification, however, has been dis- 

 puted, so that further evidence is desirable. Most of Herr 



^ The ambiguous word «f7;)f/i'/- is used. Perhaps some day Continental geologists 

 will put an end to a long-stan(ing confusion by using one term for a cleaved, another 

 for an uncleared rock. Here, I expect, the rocks are commonly slates. 



