FRESH-WATER STREAMS;. 



641 



represented in Fig. 1078 is from one of the excellent, photographs- of . scenes in the 

 Colorado region taken by the artist of Powell's expedition. It is a view of "Marble 

 Canon " — a part of the gorge, fifty-five miles long, extending from the mouth of the 

 Paria to the mouth of the Little Colorado. The walls, in 'the distance, have a height 

 of 3,500 feet. It shows that the profound channel is a cut through horizontally strati- 

 fied rock, and that the lofty walls have in places been chiselled down nearly to a true 

 vertical. 



Fig. 1079 is another view from the same remarkable region, illustrating especially the 

 side-canons. It is from the Report of Lieutenant J. C Ives, the commander of the ex- 

 pedition with which Dr. Newberry was connected. 



Newberry attributes these profound gorges, and beyond doubt correctly, to erosion, 

 each stream having made its own channel. The cliffs are so high that in general no 

 undermining can set back the walls far enough to allow pf alluvial plains along the 

 bottom, even when the water is not too rapid; and, when a channel is cut in granite, 

 lateral wear is always small. 



In the more distant part of Fig. 1079, there is a higher level of rock, — the overlying 



Fig. 1078. 



Canon of the Colorado. 



gypsiferous red sandstone, probably Triassic or Jurassic (p. 407). It is in isolated 

 tables, and in some places in columns, needles, and towers, the greater part of the 

 formation having been swept off by erosion, due partly at least to fresh waters. Still 

 farther to the east, beyond the range of the view, another more elevated level is 

 formed by Cretaceous strata : the existing surface-features are similar to those of the 

 older red sandstone. 



Ovvin" to the rapid increase of ratio in the power of running water, 

 41 



