GEOLOGY AND TOPOGRAPHY OP HAWAII. 119 



A matter of considerable interest has been brought to light through the ex- 

 cavations and road-cuttings about the base of Diamond Head, and especially 

 at the quarries and sand pits opened there. The material of the lower slope is a 

 talus made up of angular fragments from the slopes above, which is cemented 

 into a brecciated mass, showing clearly that none of the angular i)articles have 

 been rounded against each other, or by the action of water. In this mass have 

 been discovered the remains of land shells of several probably extinct species 

 belonging to well-known genera. Dr. Hitchcock concludes that the talus breccia 

 at Diamond Head must be much newer than the date of the eruption of the 

 tuff, since it is composed of fragments of that material from the older eruptions 

 that are cemented together in the more recent talus. Considerable time must 

 have elapsed between the ejection of the older material and the presence of the 

 shell-bearing animals because the rocks must have been decomposed sufficiently 

 to admit the growth of some vegetation on which the mollusks could live. From 

 observations made in the same vicinity, and data gathered elsewhere a])()nt the 

 island, but principally from the remains of the marine shells distributed inland 

 over its surface, the same authority concludes that the whole of the island of 

 Oahu must have been subsequently submerged for a brief period to a depth of 

 two to three hundred feet, presumably during the Pliocene period. If so, it 

 is concluded that the time of deposition of the land shells, found at the foot 

 of Diamond Head, will be fixed at a period sufficiently remote to admit enough 

 time to have elapsed since then to account for the development elsewhere on 

 the island of the related and varied forms of land and tree shells^ which, 

 as we shall find in another chapter, have been much studied by many zoologists, 

 but especially by the world-renowned evolutionist, Dr. John T. Gulick, whose 

 pioneer work in that important field of science has added so much th;;t is funda- 

 mental to our understanding of the great laws of organic evolution. 



Geologic History of Oahu. 



In the preceding pages only a meager outline of the written evidence touch- 

 ing on the more salient points in the geologic history of Oahu has been at- 

 tempted. Enough of the wonderful story has been given, however, to malvc it 

 appear that the island was not in existence in its present form at the beginning, 

 nor was it thrown up in its present form in a single mighty titanic convulsion 

 of nature. 



Let us review in their apparent natural order, some of the important chap- 

 ters in nature's history of Oahu, for the facts which tell of the hoary events 

 resulting in the formation of this wonderful island, with its charming scenery, are 

 all written in stone, as it were, and may be read by those with skill and patience 

 to decipher. 



In the beiziniiing the long Pacific Ocean swells doubtless rolled wiUkmiI 

 interruption over the place where the island now stands. Just how hum' this 

 condition lasted we can never know, but tlie evidence seems sufficient to I'rofessor 



^ AchutineUidm. 



