SCENERY OF SWITZERLAND. 
198 
on the east and north-east. The tufa contains 
angular fragments of Jurassic rock, but no trace of 
any post-tertiary deposits. They are therefore post- 
jurassic; but although we find basaltic bombs, lava 
tears, ashes, etc., looking so fresh that one might 
suppose them to belong to an existing volcano, it is 
evident that the period of activity had already ceased 
before the glacial period. 
Below the Lake of Constance the Rhine ran no 
doubt nearly in its present course even before the 
glacial period, but not exactly. 
At one time it seems to have occupied the broad 
and now deserted valley of Klettgau. The present 
course has many marks of being comparatively 
recent. 
Hence the bars of rock, one of which causes 
the celebrated and magnificent fall at Schaffhausen. 
The ridge regulates the height of the Lake of Con- 
stance, which would have been much lower if the 
Rhine had been running in its former bed. 
The play and change of colour at the falls is 
wondeiful. In the early morning, as I have seen it 
from the Neuhausen side, the river above the falls 
looked like a smooth, undulating table of rock, from 
the ledge of which the water suddenly seemed to 
leap , as if the rock w'ere struck by a Prophet. As 
