WATER AS A MECHANICAL AGENT. 



179 



The earliest stages are well illustrated in the Hawaiian mountains. One 

 of them, Mount Loa, 13,675 feet high (see Figs. 227 and 229), is still active ; 

 consequently it is without river valleys or gorges. Another, Mount Kea, 

 13,805 feet, has many gorges on the wet or windward side, extending upward 

 from the coast, where they are several hundred feet deep ; but they go only 

 half-way to the top. The leeward side is yet unchanneled. 



The map here introduced is that of the adjoining island of Maui. 



160. 



On eastern Maui, the cone, 10,000 feet high, has a somewhat less recent 

 aspect in its rocks than that of Mount Kea. It has channels on its wind- 

 ward slopes, some of which reach up to the edge of its great crater ; but on 

 the leeward side only narrow trenches that seldom contain water. At the 

 same time, western Maui, nearly 6000 feet, has profound valleys in place of 

 the many small ones, marks of very long exposure to denuding agents ; and 

 another island of the group farther west, Oahu (Fig. 257), is like Maui in 

 having a western volcano in ruins, — a few crests and profound valleys in 

 place of even slopes, and an eastern volcano of much more recent aspect, 

 though more gorged than eastern Maui. But it met with a disaster in which 

 over half of its mass sunk beneath the ocean, leaving a precipice for 20 miles 

 facing the northwest or to windward. The nearly vertical surface has con- 

 sequently a range of alcoves, finely illustrating this style of mountain archi- 

 tecture. To the northward the alcoves are lengthened into gorges. Moreover, 

 over eastern Oahu the winds pass the summit of the precipice before the cold 

 heights have deprived them of their moisture, so that the leeward slopes take 



