374 GNEISS RESTING ON STRATA. 



the west of the Schwarzwald and Bohmerwald. Gneiss is an im- 

 portant rock in Central France, and it forms much of Scandinavia 

 and Finland. With these rocks are grouped the gneiss which skirts 

 the coast of Brazil, and that which constitutes the Laurentian rocks 

 of Canada. 



The gneissose rocks of the Outer Hebrides and "West Coast of Scot- 

 land were first distinguished by Sir E. I. Murchison as " fundamental 

 gneiss ; " and he subsequently endeavoured to identify the rock with 

 the Labrador series of Canada. This gneiss extends from Cape 

 Wrath to Loch Broom, Loch Maree, and Loch Torridon ; and here, 

 as in the long island of the Hebrides, it is a mass of granitoid gneiss, in 

 which hornblende and quartz are much more important than felspar 

 and mica. Its strike is from north-west to south-east. 



Gneiss which Rests upon Stratified Rocks. North-east of Chem- 

 nitz and west of Freiberg three large masses of gneiss, many thousand 

 feet thick, extend in a line. They rest upon Silurian slaty rocks, and are 

 covered by carboniferous conglomerate. Gneiss extends about Munch- 

 berg, north-west of the Fichtelgebirge,and fills an elliptical basin of eight 

 square miles in the newer clay slate. The gneiss appears to rest 

 unconformably on the rocks beneath. This condition is attributed by 

 G umbel to inversion, but is sometimes supposed to indicate a younger 

 gneiss. In West Finnmark a thick gneiss rests upon clay slate, lime- 

 stone, and mica slate. In Central Norway crystalline slates rest upon 

 Silurian strata ; and David Forbes described sections above Christian- 

 sand in which bands of granite about ten feet thick alternating with 

 limestone are interstratified in gneiss. All these rocks are mixed in 

 extraordinary confusion on the Torresdale river, where foliated gneiss 

 passes into granitic gneiss, and both alternate irregularly with granite 

 and limestone. 



In the Alps, about the Col de Geant, near Mont Blanc, by the 

 Grimsel and St. Gothard, for example, gneiss is found folded between 

 beds of limestone which cannot be older than the Lias. Hence the 

 gneiss must have originated after the Lias was formed. 



Mica Schist. 



Its Origin. Mica schist, like gneiss, appears sometimes to 

 have derived its ingredients from the destruction of granitic rocks, 

 though it contains but little felspar. We may conjecture that the 

 felspar was decomposed during the disintegration of granite, and 

 mostly carried away, leaving the quartz and the mica to be arranged 

 by the water in the alternate layers which render this rock so remark- 

 able. Such ideas are readily suggested by the structure of the Mill- 

 stone grit and Carboniferous sandstones of the North of England ; 

 though its association with granite favours the belief that it originated 

 under similar conditions. 



The foliation of mica schist is subject to much unevenness in 



