244 
THE GEAND CAKOE DISTEICT. 
streams is often in excess of the actual lifting power of the water, and a 
portion of it is deposited. But in the Marble and Grand Canons this is 
rarely so. The flood-w'ater comes from far distant regions. In the Glen 
Canon, where the declivity is notably less, any excess of load above the 
quantity easily transported (if any such excess ever occurs) is temporarily 
deposited. Reaching the Marble Canon the greater declivity at once aug- 
ments greatly tlie transporting power, and the torrent sweeps everything 
loose before it For six or seven weeks the corrasion goes on at a very 
rapid rate. Many reaches, which at low water are protected by sand and 
gravel, are swept bai’e, and for a time are subject to the full corrasive 
energy of the torrent. The water rises from 30 to 60 feet, attacking the 
slopes at the bottom of the gorge, which are ordinarily naked rock, and 
grinding them away at a rate which must be a rapid one during the time it 
is in operation. 
Reverting here in a summary way to the two classes of rapids formed 
in the river, we find that they are due to two wholly distinct causes — 1st, 
to the unequal hardness or resisting power of the strata in the bed of the 
stream; 2d, to the accumulation of piles of large fragments washed in 
through the lateral gorges. The greater number of rapids are due to the 
latter cause. The general characters of the two kinds, however, are strik- 
ingly different. Those which occur in the hard crystalline rocks are very 
long, and with some notable exceptions are less violent and headlong than 
the others, but they are also complicated with the second class of rapids, 
%. e., those due to the bowlders rolled in from the side chasms. If we sepa- 
rate the latter effects, we find the effect of hardness of the strata to be a 
general increase of slope distributed with some approach to uniformity over 
many miles of length of the river bed. It is plainly so in the Kaibab and 
Sheavwits, and this effect is not at all obscured by the joint operation of 
both causes. The rapids of the second class are short and violent, as might 
have been inferred from the nature of the cause which produces them. 
