5U Prof. T. G. Bonnet/— The Effect of Pressure 



siderable resemblance to the dark serpentine from north of Cadgwith 

 (Lizard), or to those found near Genoa or at Levanto. 1 



One of the largest masses of serpentine in the Alps occurs near 

 the watershed of the Pennine Chain in the neighbourhood of 

 Zermatt. In this region mountain-making has taken place on a 

 grand scale, so that good opportunities are afforded of studying the 

 effects of pressure as an agent of metamorphism. But before 

 considering this, a few words of explanation are necessary for the 

 sake of those who are not familiar with the geology of this region. 

 The snowfields in the neighbourhood of Monte Rosa, upon the 

 north-western side of the watershed, descend towards the Visp in 

 two glaciers — the Gorner and the Findelen — which are separated 

 by a huge buttress or spur. This culminates in a rocky ridge which 

 runs parallel (roughly from east to west) with the former glacier. 

 At its western end is a singular craggy tower, named the Eiffelhorn 

 (9616 feet) ; east of this, the ridge after a depression mounts to the 

 well-known Gorner Grat (10,290 feet), from which it undulates 

 upward along the Hochthaligrat (10,791 feet), and finally culmi- 

 nates in the Stockhorn (11,595 feet). 



This huge spur to a great extent consists of serpentine ; but on 

 its northern shoulder a considerable area (above the Riffelhaus Inn, 

 8430 feet) is occupied by a tolerably hard fine-grained green schist, 

 apparently bedded, in which a rather acicular hornblende and some- 

 times epidote are fairly conspicuous. 2 This mass is completely 

 surrounded by serpentine. The latter rock continues to the 

 summit of the Gorner Grat, where it is succeeded by calc-mica 

 schists, associated with some fissile mica-schists and micaceous gneiss 

 and with a hard white quartz-schist. This group — on the details 

 of which it is, for the present purpose, needless to dwell — is 

 followed, apparently in descending order, by a moderately coarse, 

 rather micaceous, gneiss, of which, so far as I have seen, the 

 remainder of the ridge, up to the peak of the Stockhorn, consists. 

 The annexed section (Fig. 1), which is merely diagrammatic, may 

 serve to render the relation of the rocks, described above, rather 

 more clear. 3 



The serpentine no doubt forms part of the bed of the Gorner 

 glacier, for of it, on the left bank, not only the rocks of the Lychen- 



1 See Geol. Mag. Dec. II. Vol. VI. p. 362 ; Vol. VII. p. 538. Descriptions of 

 some Alpine serpentines will be found in Mr. Teall's British Petrography, p. 109, 

 et seq. 



2 A specimen of one of the harder varieties which I have had sliced consists of a 

 not very characteristic glaucophane (the greater part of the grains being, as has often 

 been described, altered into a dull green hornblende), epidote, garnets (rather small), 

 a little white mica, hematite, etc. It is difficult to offer an opinion as to the origin 

 of these green schists. Some may be modified igneous rocks ; others possibly altered 

 tuffs. 



3 A ccording to the Swiss Geological Survey there should be some rauchwacke 

 interstratified near the base of the quartzite, but I omit this rock as I do not hold 

 it to be a member of the crystalline series. The quartz-schist, green-schists, and 

 calc-mica schists belong to the great group of crystalline schists which in the Alps 

 have such a wide distribution and occur at the top of the Crystalline (probably 

 Archaean) series. 



