124 NATl HAL lilSTOKY OF HAWAII. 



time a f..ivstt-.l .•..n.KH-tiuii was e'stal.lished l)"lwoen the two Oaluian centers of 

 evolnti.Mi. f..n..in- a fannal bridge ^vhi.-h mln.itted of the mingling of the two 

 ishmd I'aimas. WhWr Hie hind connection endi-ivs the forest has, in recent time, 

 become extin.-l an.l tlnis the two centers are again isolated so far as forest- 

 h)\iiii: snails are concerned. 



Tni-ning to the eastern or Molokai-Lanai-Mani region it is Dr. Pilsbry's 

 opini.m that the elose relali..nshi|. of their fanna indicate that they formed a 

 sinude island up to late I'li.n-ene or even Pleistocene time. The formation of 

 the ciiannels between Molokai, Lanai and !\lani mnst be considered as a very 

 recent event since they stand on a i^latfonn wilhin the 100 fathom line and their 

 fannas are very closely related. 



The investigation of the island fauna and flora as conducted by various ob- 

 servers has l)rought out facts of evolution that seem in full accord with the dis- 

 niemlierment of the various islands as here described. 



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

 the dcc|)ly eroded valleys, the submerged coral reefs all tend to bear out the 

 l,r..ad conclusion that the group has evolved by the submergence of a single 

 island, and that the isol;;tion of the existing islands, with their peculiar, yet re- 

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

 nants on tl Ider and dec|)ly subsided larger bind area. 



Dr. Seivno liishop. discussing the geology of Oahu, tentatively offered an 

 estimate of the leiii^th of time that must have elapsed since the successive events 

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

 time nnist of necessity be accepted only as individual guesses and the personal 

 factor taken into acc(»niit. but they have their value for those less skilled, enabling 

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



While scientiiic 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 AA^aianae Range as a volcanic mountain at 

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

 eight huiidi'ed thousand years ago, and the extinction of the AVaianae activity one 

 Inuidred thousand years thereafter, Avhile the extinction of the Koolau Range is 

 placed live hnmlred thousand years back in the past. The emergence of Laeloa 

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

 Tlie time of the eruption of Punchbowl is given as forty-five thousand years ago: 

 the small Xuuanu craters twenty thousand; Diamond Head fifteen thousand; 

 Kainniki twelve thousand: the Salt Lake group ten thousand; Tantalus, seven or 

 eight thousand, while the eruption of the Koko Head group, the last of the im- 

 portant tuff-cones to be formed, is given as occurring but a meager five thousand 

 years ago. The ant hoi-, however, is inclined to attribute a very much greater 

 age to Oahu than that indicated by Dr. Bishop. TIk^ fouiulation for sucli 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 practi- 

 cally completed as they are now before the slight re-elevation of the island 



