124 NATURAL HISTORY OF HAWAII. 



time, a forested connection was established between the two Oahuan centers of 

 evolution, formino- a faunal bridge which admitted of the mingling of the two 

 island faunas. While the land connection endures the forest has, in recent time, 

 become extinct and thus tlie Iwo centers are again isolated so far as forest- 

 lo\ ing siuiils are concerned. 



Turning to the eastern or Molokai-Laiuii-Maui region it is Dr. I'ilsbry's 

 opinion that the close relationship of their fauna indicate that they formed a 

 single island up to late Pliocene or even Pleistocene time. The formation of 

 the channels between Molokai, Lanai and Maui must be considered as a vei'v 

 recent event since they .stand on a platform wilhin the 100 fathom line and their 

 faunas are very closely related. 



The investigation of the island faniui and tlora as conducted by vai'ious ob- 

 servers has brought out facts of evolution that seem in full accord with the dis- 

 memberment of the various islands as here described. 



In addition to all else the evidence of the wonderfully dissected mountains, 

 the deeply eroded valleys, the submerged coral reefs all tend to bear out the 

 broad conclusion that the group has evolved by the submergence of a single 

 island, and that the isolation of the existing islands, with their pecidiar, yet re- 

 lated plants and animals, have been formed as superimposed volcanic repi- 

 nants on the oldci' and deeply subsided larger land area. 



l)i-. Screno i^ishop, discussing the geology of Oahu, tentatively offered an 

 estimate of the length of time that must have elapsed since the successive events 

 in the geological history of the island took place. Such estimates of geologic 

 time must of necessity be accepted only as individual gue.sses and the personal 

 factor taken into account, but they have their value for those less skilled, enabling 

 them to form a rough chronology that the mind can in a measure grasp. 



While scientific guesses of this nature are valuable, they are liable in each 

 instance to fall far short of the actual time involved. Dr. Bishop's table places 

 the time of the emergence of the Waianae Range as a volcanic mountain at 

 one million years ago. The emergence of the Koolaii Range is placed at 

 eight hundred thousand years ago, and the extinction of the Waianae activity one 

 hundred thousand years thereafter, while the extinction of the Koolau Range is 

 j)laced five hundred thousand years back in the past. The emergence of Laeloa 

 craters and Rocky Hill are both placed at least seventy-flve thousand years ago. 

 The time of the (n-uption of Piuichbowl is given as forty-five thousand years ago: 

 the small Xunniiu crntcrs 1\vcn1y thousand; Diamond Head fifteen thousand; 

 Kaimuki twchc thousand; the Salt Lake group ten thousand; Tantalus, seven oi- 

 eight tliousand, while the eruption of the Koko Head group, the last of tlu' im- 

 portant tuft'-coiies to be formed, is given as occurrint;- but a nu^ati'er five tlmusauii 

 years aiid. The author, however, is inclined to attribute a very nuu-h greater 

 age to Oahu than that indicated by Dr. Bishop. The foundation for such a belief 

 is based largely on a careful physiographic study of the Waianae Mountains. It 

 seems obvious that the deeply eroded valleys of the Waianae Range were prai-ti- 

 cally c(iiii|ilete(l as they are now l)efni'e the slight re-elevation of the island 



