Schistose 'Greenstones ' from the Pennine Alps. 149 



schists ' (both badly exposed), followed by much Dark-mica schist, 

 often containing black garnets. Higher up is a considerable mass of 

 Jurassic rock with the ' knots ' and ' prisms ' which have been mis- 

 taken for garnets and staurolites, but Dark-mica schists set in again 

 before the summit is reached. They continue down the southern 

 flank of the peak ; but rather north of the lowest part of the water- 

 shed, between Switzerland and Italy, the ' Disthene-schist ' is again 

 found, followed by a fair-sized mass of rauchwacke. 



The return section gave a similar association in reverse order ; 

 and both confirmed the conclusions expressed by the author in 1890 

 as to the absence of garnets and staurolites from Jurassic rocks (with 

 belemnites &c), and the great break between these or the under- 

 lying rauchwacke (where it occurs) and the crystalline schists, in 

 which garnets often abound, of the Lepontine Alps. The crystal- 

 line schists and the Mesozoic rocks are thrown into a series of very 

 sharp folds, which, locally, presents at first sight the appearance of 

 interstratification. 



2. "On some Schistose 'Greenstones' and allied Hornblendic 

 Schists from the Pennine Alps, as illustrative of the Effects of 

 Pressure-Metamorphism." By Prof. T. G. Bonney, D.Sc, LL.D., 

 F.R.S., Y.P.G.S. 



The author describes the results of study in the field and with 

 the microscope of (a) some thin dykes in the calc-schist group, much 

 modified by pressure ; (b) some larger masses of green schist which 

 appear to be closely associated with the dykes; (c) some other 

 pressure-modified greenstone dykes of greater thickness than the 

 first. The specimens were obtained, for the most part, either near 

 Saas Fee or in the Binnenthal. 



These results, in his opinion, justified the following conclu- 

 sions : — 



(1) That basic intrusive rocks, presumably once dolerites or basalts, 

 can be converted into foliated, possibly even slightly banded, schists, 

 in which no recognizable trace of the original structure remains. 



(2) That in an early (possibly the first) stage of the process the 

 primary constituents of the rock-mass are crushed or sheared, and 

 thus their fragments frequently assume a somewhat ' streaky ' order ; 

 that is to say, the rock passes more or less into the ' mylonitic ' 

 condition. 



(3) That next (probably owing to the action of water under 

 great pressure) certain of the constituents are decomposed or 

 dissolved. 



(4) That, in consequence of this, when the pressure is sufficiently 

 diminished, a new group of minerals is formed (though in some eases 

 original fragments may serve as nuclei). 



(5) That of the more important constituents hornblende is the 

 first to form, closely followed, if not accompanied, by epidote ; next 

 comes biotite (the growth of which often suggests that by this time 

 the pressure is ceasing to be definite in direction), and lastly a water- 

 clear mineral, probably a felspar, perhaps sometimos quartz. 



