204 Geological Society: — 



only modified igneous rocks, these are associated with recognizable 

 igneous rocks of later date. 



(2) There are, speaking in general terms, three great rock-groups 

 in the Alps which simulate curiously, if they do not indicate strati- 

 graphical sequence. The lowest and oldest resembles the gneisses 

 of the Laurentian series ; the next, those rather " friable " gneisses 

 and schists called by Dr. ^terry Hunt the Montalban series ; the 

 third and uppermost is a great group of schists, generally rather 

 fine-grained, micaceous, chloritic, epidotic, calcareous and quartzose, 

 passing occasionally into crystalline limestones, and (more rarely) 

 into schistose quartzites. 



(3) The Pietra Verde group of Dr. Sterry Hunt, so far as the 

 author has been able to ascertain, consists mainly of modified 

 igneous rocks, of indeterminable date, and is at most only of local, 

 if, indeed, it be of any classificatory value. 



(4) Of the above three groups the uppermost has an immense 

 development in the Italian Alps and in the Tyrol, north and south 

 of the central range. It can, in fact, be traced, apparently at the 

 top of the crystalline succession, from one end of the Alpine chain 

 to the other. 



(5) The middle group is not seldom either imperfectly developed 

 or even wanting, appearing as if cut out by denudation. It was 

 not seen in the traverse of the Franco-Italian Alps, except perhaps 

 for a comparatively short distance on the eastern side, being pro- 

 bably concealed by Palseozoic and Mesozoic rocks on the western 

 side. It is not very completely developed in the Eastern Tyrol, 

 and seems to prevail especially in the Lepontine Alps, and on the 

 southern side of the watershed. 



(6) The lowest group is fairly well exposed, both in the French 

 Alps and in the Central Tyrol. 



(7) As a rule, the schists of the uppermost group had a sedimen- 

 tary^ origin. The schists and gneisses of the middle group very 

 probably, in part at least, had a similar origin. In regard to the 

 lowest group it is difficult, in the present state of our knowledge, to 

 come to any conclusion. 



(8) The slates and other rocks of clastic origin in the Alps, 

 whether of Mesozoic or of Palseozoic age, though somewhat modified 

 by pressure, are totally distinct from the true schists above men- 

 tioned, and it is only under very exceptional circumstances, and in 

 very restricted areas, that there is the slightest difiiculty in distin- 

 guishing between them. The evidence of the coarser fragmental 

 material in these Palseozoic and later rocks indicates that the gneisses 

 and crystalline schists of the Alps are very much more ancient than 

 even the oldest of them. 



(9) The remarks made by the author in his Presidential Address, 

 1886, as to the existence of a " cleavage-foliation" due to pressure, 

 and a " stratification-foliation " of earlier date, which seemingly is 

 the result of an original bedding, and as to the importance of dis- 

 tinguishing these structures (generally not a difficult thing), have 

 been most fully confirmed. He is convinced that many of the con- 



