QUANTITY OF SEDIMENT TEANSPOETED. 
237 
burst its dam and discharged its waters. As it moves onward it sweeps 
everything loose in its way. Huge fragments of tons weight fallen from 
the cliffs above are bowled along with a facility that is highly suggestive. 
The water is charged to its utmost capacity with fine sand and silt, and it 
is somewhat surprising to see how much of this stuff a given quantity of 
water can carry. In the Mesozoic rocks it would not be an improbable esti- 
mate to say that these spasmodic waters carry nearly three times their own 
volume of fine material, and it is quite certain that they often carry more 
than twice their volume. Every explorer in this region can recite expe- 
riences of trying to obtain from some of the rills water for camp use by 
allowing a kettle-full to stand over night in order to settle, and finding in 
the morning an inch or two of dubious water on the surface of the vessel, 
with 7 or 8 inches of viscous red clay beneath and 3 or 4 inches of sand and 
grit at the bottom. The sediment thus transported is sand and clay. The 
rocks of the Mesozoic system are composed almost wholly of these two 
materials, the calcareous members being very few and of very small thick- 
ness ; and such of the latter as occur are more frequently gypsum than 
calcite. The Permian also is similarly constituted, though having a few 
notable bands of arenaceous lime^one. The cementing material of the 
sandy-clayey beds of the Trias and Permian is more or less gypsiferous, 
and many of the layers are highly charged with selenite. The ready 
solution of this cement yields an abundance of sand and clay in highly 
comminuted form, and every copious shower washes it along in great 
quantity. 
The amount of this finer material which reaches the Colorado in the 
canons is very great : and what is most striking, the contributions are not 
extremely irregular. In the summer time local showers, though infrequent 
in any given locality, are frequent enough in this portion of the Plateau 
Country as a whole. From any commanding point, which overlooks a 
very great expanse, distant showers may be seen on very many days of the 
hot summer. If we were to spend a week on such a point we might reckon 
with a high degree of probability upon one or more days in which heavy 
showers would be visible in different parts of the panorama. They are, 
however, extremely local, and rarely cover such large extents of country as the 
