8o PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



To the age of the metamorphism, and the part to be assigned to 

 pressure, I shall presently return. I will now only notice one 

 point in close connexion with the above conclusions, viz. the indi- 

 cations of unconformity. In a complicated mountain-region such as 

 the Alps we cannot lay much stress upon local changes of strike. 

 Indeed, so far as I have observed, the dominant strike often con- 

 tinues over large areas with remarkable uniformity. Neither must 

 we rely too much upon the absence of a series of beds, and an appa- 

 rent break in the order of succession, because, as eyerj one knows, 

 extraordinary results may be produced by overthrust-faulting in 

 folding, or by folding of beds previously faulted. At the same time 

 what I have myself seen leads me to suspect that there is very com- 

 monly a break between (3) and (4) ; not perhaps universally, for 

 in the Gothard-Lukmanier region it appears to me difficult to say 

 where the line between the two is to be drawn ; but I find it very 

 hard to explain the distribution of (4) in the Central and Western 

 Pennines, as indicated in the maps of the Swiss surveyors and as 

 known to myself, unless we suppose that at least (3) is sometimes 

 even wholly wanting. More than this I will not at present say ; 

 but it is quite possible that other unconformities may be hereafter 

 discovered *. 



* As there are no names which are yet generally recognized, and the groups 

 themselves are not, and perhaps never can be, very clearly defined, it may 

 render the above description more comprehensible if I exhibit in a tabular form 

 the rocks of this Alpine district in what appears to me their stratigraphical 

 succession, giving for each one or two of its best-defined types, and compare 

 this with the arrangements of other authors. It must be remembered that 

 some groups appear to be rather local, or are missing in certain districts. The 

 first named is the oldest. 



(a) Granitoid gneisses 



Ex. 



Antigorio gneiss (gorge of Gondo) and 

 probably central gneisses of Oberland 

 chain, 



(b) Banded gneisses Simplon Pass, S. side, and Monte Leone. 



(c) Micaceous gneiss Lepontine gneisses. 



{d) Mica-schists (with garnet &c.) Tremola schists. 



(e) Schists (variable) Piora schists (below the melanite schist). 



r The schists above the melanite schist in 

 4. (/) Brown-bedded schists -I the Lukmanier region : the Binnen- 



[ thai-schists. 



Other Classifications : — 



Lory. 

 n • f Granitoid. 1 -i 7 



^^^^^n Laminated. I =^^"^^- 

 ^j- ( Mica-schists, often j 



i • N garnet-bearing, alter- I =ca,ndd. 

 [ nating with gneiss. J 

 rp 1 f Also chloritic and 1 -, ^ 



^f^; hornblendic, withh^f^y 

 «^'^^^H gneiss-like rock. J ^P*" ' )" 



Grey [ Also quavtzites 'i =/ (pt. ?) 

 lustrous < and gypsums, I and later 

 schists. L &c. J rocks. 



VoN Hauer, 

 Gneisses = a and b. 



Greenish schistose rock. 

 Saccharoidal limestone. 

 Chloritic and talcose rocks. 



Eecent gneiss 1 _ ^ 



Mica-schist '' ~ ' • 



Schists (hornblendic, ] _ ^ 

 calcareous, &c.) _) ~'^* 



