THE RHINE. 
187 
of Dissentis are the remains of an ancient forest. 
The stumps of the trees, which are still upright, 
have in some places been exposed by denudation. 
As in the case of the Rhone, so also here, the 
Swiss maps fait to convey a clear idea of the 
geological features, though for this they are not to 
blame. They gave a separate colour for the Bilndner- 
schiefer on the south of the river, in which no fossils 
had been found, and the relations of which were 
consequently uncertain. Recent researches, however, 
indicate that some of these schistose rocks belong 
to the Jurassic period, and correspond with the 
strata on the left of the river. 
The Vorder Rhine, which may be considered as 
the true Upper Rhine, is generally stated to have its 
source in two small lakes, the Lake de Siarra, and 
the Lake Toma on the north flank of the Sixmadun. 
The tributaries which the Vorder Rhine receives on 
the north side are of secondary importance (see vol. i. 
p. 214 ), but on the south it is joined by the Mittel 
Rhein at Dissentis, the Somvix at Somvix (Summus 
vicus, the uppermost village), the Valser Rhein or 
Glenner at Ilanz, the Rabiusa near Versam, the 
Hinter Rhein at Reichenau, the Plessur at Chur, the 
Landquart near Maienfeld, and the 111 near held- 
kirch. The Rhine repeats to a certain extent, and 
