ANI^IVERSAEY ADDRESS OF THE PRESIDEIs'T. 69 



iSr.E. strike) is the result of crushing, subsequent to which there have 

 been local disturbances. 



It cannot, I think, be doubted that the above group of rocks 

 passes under the Mesozoic series ; and no member of the latter 

 indicates any approach to a foliated structure, though a rude cleavage 

 is often conspicuous. 



On the south side of the Maderanerthal, mounting to the Brunni 

 Pass, we found gneisses, which were sometimes moderately schis- 

 tose, at others almost as granitoid as those near Wasen, on the 

 St. Gothard. About 1800 feet above the Maderanerthal hotel was 

 a gneissose rock, which, however, contained abundant well-defined 

 felspar-crystals about 1 inch long, and included fragments of a dark 

 (probably hornblendic) rock. Bands occur of a rock resembling 

 felstone or porphyroid, probably squeezed dykes, and some more 

 distinctly schistose, which, however, may very well be of a like 

 origin. In fact I saw nothing, from the opening of the upland glen 

 leading to the Brunni Pass to beyond the summit, which I could 

 regard as indubitable proof of stratification, though there were occa- 

 sionally very slabby or schistose bands, as, for instance, at the 

 summit of the Pass ; these, however, on closer examination, appeared 

 to be merely crushed-up gneiss, and the surface of conspicuous 

 foliation is only a " sheen " surface. They all show very nearly the 

 same strike, viz. between W.S.W. and S.W., and I may make the 

 same remark of all the rocks which we saw on our descent until 

 within a short distance of Dissentis. 



It results, then, that while along the western end and a part of the 

 northern and southern fringe of this huge ellipsoid of crystalline 

 rock there are appearances which are difficult to explain, except 

 upon the theory of some kind of precipitation or stratification of the 

 original constituents, there are none over the inner and greater 

 portion which we can safely trust ; but the schistose and gneissose 

 structure, with its uniform strike and high dip, is almost certainly 

 the result of pressure, and thus is an instance of cleavage- 

 foliation. 



I turn now to the great trough which bounds this orographic 

 system on the south. Almost immediately on entering the open basin 

 of the Urnerboden, we find a quartzo-micaceous limestone, highly 

 crystalline, intercalated among fissile mica-schists, which are fol- 

 lowed by a great series of schists — micaceous, chloritic, &c. These 

 have evidently been modified by the action of pressure, sometimes to 

 an extraordinary degree, subsequent to their becoming true schists ; 

 they are in places almost as fissile as slates, and the predominance of 

 " sheen surfaces " has obliterated earlier structures, nevertheless we 

 observe in the outcrops and sections such marked mineral differences 

 among diff'erent masses, that it is impossible to avoid attributing 

 them to original differences in the materials of which they are com- 

 posed. This series is referred by the Swiss geologists to the 

 Casanna schists — a series which, whatever may be its precise defi- 

 nition or geological equivalence, is universally regarded as decidedly 

 more modern than the central gneiss. It can be traced for many 



VOL. XLl I. Cf 



