Topography of the Pemiine Alps. 329 



depending on this part of the central ridge. The glacier of 

 Schwarzwakl, at the foot of Monte Moro, near lake Matmark, 

 brings numerous blocks of serpentine from the bottom of the 

 upper valley of Saas, among which two enormous masses are 

 observed, left, a few years ago, on the border of the path by 

 the glacier, the most considerable of which is looked upon as 

 the largest erratic block known. Some other sites, further 

 down near Vieges, are of less importance. 



With regard to the euphotides, M. Guyot adds to what he 

 had formerly stated regarding their original site, that he is 

 convinced their point of departure is the rocks which over- 

 look the upper part of the glacier of Alalein, particularly on 

 the left side and a little below the highest summits. The 

 eclogites, not so strictly localised, pass along the western de- 

 clivity, and descend by the moraines of the glacier of Fin- 

 elen, in which M. Guyot collected many varieties. 



The gi'eatcr part of the serpentine debris has therefore 

 descended by the valley of St Nicolas, a small quantity only 

 by that of Saas. The reverse of this holds true Avith the 

 eclogites. The euphotides come exclusively from the valley 

 of Saas. 



M. Guyot terminates his communication by a few petro- 

 gi'aphic considerations on the two groups of the Pennine 

 rocks and the rocks of Mont Rosa. A frequent comparison 

 of the various species and their numerous varieties, as well 

 as an inspection of their respective sites, leads him to think 

 that their association into two distinct groups, is not only a 

 geographical fact, as the names he has given to each of 

 them would induce us to believe, but that it is justified also 

 by their nature. He is induced to believe that these groups 

 really fonn two metamorphic series, and he mentions that he 

 has numerous specimens in bis collection, which slsewtlic al- 

 most insensible transition of the species of each of these two 

 groups into one anotlier. He likewise exhibits many speci- 

 mens obtained in situ, of each of these species, represented 

 by tlieir most widely diffused typos, and compared M'ith 

 specimens collected in an erratic state in the different parts 

 of the basin of the Rhone, whose conipkte ideiitiiy with tlic 

 first is obvious to the least experienced eye. 



