212 
SCENERY OF SWITZERLAND. 
one another, and is divided, moreover, into horizontal 
layers at tolerably regular intervals of 3 to 6 feet. 
This structure gives it a tendency- — also present, 
though less pronounced, in the Gneiss— to break into 
six-sided blocks. The Gneiss of the Ticino has a 
similar character.* 
It is evident that the valley of the Reuss is a 
valley of denudation, and the factors which have 
determined its present configuration are rain and 
water, ice and frost, the character and structure of 
the rock, and lastly, the Reuss itself. The strata 
strike somewhat obliquely across the valley; they are 
nearly vertical, and differ greatly in hardness, form- 
ing reefs across the valley. These ridges divide the 
valley into a number of small basins. They dam 
back the water, which gradually saws through them, 
and then with comparative rapidity drains the basin 
above. Rutimeyer represents the phases of this 
sequence in the accompanying diagrams, representing 
sections of the valley, which repeat themselves over 
and over again. 
^ Fig- 143 ; I; the river is sawing through the 
rock. When this is accomplished, the process of 
widening begins and debris fall down from the sides 
(Fig. 143, II^. Gradually the valley becomes occupied 
* RoUe, Beitr, z, Geol. IC. d, Schw,^ L. xxin. 
