7.8 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the second or less granitoid type, as extending from the north flank 

 of the Ofenhorn to Monte Leone, and my examination of these two 

 points led me independently to refer the rocks to the same general 

 series, one to which I should be disposed to assign a rather earlier 

 date than to the Lepontine gneisses of the St. Gothard and Lnkmanier. 

 In descending the northern side of the Simplon Pass we traverse the 

 zone of the brown-bedded schists, while close to the Ehone valley 

 there is a dark, slaty, and not much-altered rock, associated with 

 gypsum and dolomite, which is probably a remnant of a trough of 

 much later rock. Carboniferous or Secondary. 



In like manner the Pennine Alps about the head waters of the 

 Yisp and of other tributaries of the Ehone immediately to the 

 west, in the main consist of a fundamental mass of coarse gneiss, 

 but rarely exposed, which passes up into finer-grained gneisses. 

 To one or the other of these the peculiar AroUa gneiss probably 

 belongs. These are followed by a great group of mica -schists and 

 fine-grained gneisses, which now and then recall to mind the Tre- 

 mola schists, and these, again, are overlain by bedded green and grey 

 schists — ^^chloritic, hornblendic, and micaceous — which are regarded, 

 I have no doubt rightly, as members of the same 'general group as 

 the brown-bedded schists already mentioned, that is the schistes 

 lustrees of many authors. In this district, towards the S. and S.W., 

 green schists are much more 'frequent than further east ; but it is 

 more than probable that some of them are merely crushed igneous 

 rocks. Others, however, both field evidence and microscopic exami- 

 nation lead me to consider as originally sedimentary. 



Passing up the Dora Ealtea from Ivrea, and neglecting some 

 rocks obviously of igneous origin, we traverse gneisses which have 

 a general resemblance to those already described on the southern 

 flanks of the Lepontine Alps, and then enter micaceous, chloritic, 

 and other green schists, resembling those of the Zermatt region. 

 The valley of the Dora Baltea, below Aosta, cuts gradually through 

 a great zone of these newer schists, and the road to the St. Bernard 

 does not pass away from it until we are about halfway to St. Eemy. 

 Hence to the summit of the St. Bernard and thence to the neigh- 

 bourhood of Liddes our course lies over schists of a stronger cha- 

 racter. Mica-schist is the dominant rock. This is often silvery, 

 but sometimes darker greenish varieties are also found, together 

 with chloritic or actinolitic schists, and fine-grained gneisses. On 

 the southern side of the pass silvery schists, with garnet and with 

 andalusite, are not rare. All these are referred by the Swiss geo- 

 logists to the Casanna group, and they not unfrequently recall to 

 mind the Tremola schists of the St. Gothard and Yal Piora region. 

 . On the highest part of the pass there are some " augen-gneisses," 

 but these may be only crushed intrusive granite. The rock also on 

 the northern side has often a more gneissic character than that on 

 the southern. 'Near Liddes, after passing a trough of Carboniferous 

 rock (which I have not examined), we come to very characteristic 

 grey schist belonging to the Upper (scJiistes lustrees) group ; then, 

 after crossing an infold of slatv Jurassic rock, descend to the Ehone 



