GEOLOGY AND TOPOGRAPHY OF HAWAII. 131 



]\Iakapuu Points, are features of an excursion thither that arc always much en- 

 joyed, while the picturesque coral bay at Ilaiiauiua, and the unmistakable evi- 

 dence of the nature of the formation of the bay, presents a variety of objects well 

 worthy of a visit. 



Along- the coast, beyond Diamond Head, at Waialae Bay, are a number of 

 fresh water springs on the edge of the ocean, and at the end of Black Point 

 is a sea cave with a large hole through the roof, from which water and spray 

 s])urt thirty or forty feet in the air during rough v/eather. As has been 

 intimated, the sea slope of Diamond Head is full of geologic interest. Along 

 the beach line sand concretions, caused by organic acids, may be seen in the 

 process of forming about the roots of plants and trees which penetrate the ex- 

 posed beds. Higher up, in excavations along the line of the road, similar con- 

 cretions may be found, thousands of years old, in wdiich the roots that formed 

 the center have been completely fossilized. 



Pot-holes in the rock along tlie reef are especially numerous on the 

 shore at this point. Many of them are three feet or more across, and well 

 illustrate this peculiar, rather than important, feature of erosion. The scouring 

 work is accomplished 1)\- the grinding action of the sand rock fragments as tools 

 in the hands of the waves. The coral reef between Waikiki and the mouth of 

 Honolulu Harbor is a complete laboratory in reef formation. Seen through 

 a watergiass or a glass bottom boat, the growdng, living reef, in connection with 

 the elevated reef farther inland, exhibits the present side by side with the dim 

 past, and shows every phase of this living agent that has i)layed so important 

 a part in the geologic history of the group. 



A half day's ramble over the slopes of Punchbowl and down along the 

 nearby Nuuanu Stream will reveal excellent examples to illustrate a hundred 

 points in structural and dynamic geology. The road ui) Xuuanu Valley, the 

 Pali, and the descent over the floor of the old Pali crater to the sea-shore on 

 the windward side of the island exhibit scores of points of interest to one who 

 cares for geology. The latteral valleys with their gauze-like w'aterfalls; ex- 

 amples of sub-aerial erosion at the Pali ; the splendid dikes displayed in the 

 solid rock by the roadside; the vertical walls of the mighty pit itself; the living 

 reef at Kaneohe; these and a thousand features like them, fill the mind with awe 

 and wonder, and the careful observer is surprised that so much can lie crowded 

 into a cross-country ride. 



The windward shore of the island at Laie exhibits the ccmibined action of 

 the sea and the wind in ]uling up dry sand inland into mounds thirty or forty 

 feet in height, and of the effect of the submergence again of such dunes under 

 the sea from whence they originally came and from Avhich they have again 

 been lifted up. At Kahana we have an excellent example of a drowneil valley. 

 At Kaliuwaa is a valley of awe-inspiring grandeur; so nari'ow and deep is it 

 that it forms a dark, narrow passage-way cut into the solid mountain that is 

 shut in with inaccessible vertical w^alls, nearly a thousand feet in height. Down 

 these basalt walls clear, cold mountain Avater has cut out siiiooDi cliannels so re- 



