NOTES ON ZOOGEOGRAPHY. 



As yet, only the Acliatinellidce and Amastridcz of all these 

 beds have been thoroughly studied, and these are the groups 

 which everywhere show the greatest local speciation, there- 

 fore less useful for comparative studies of the beds than the 

 widely distributed small shells of other families. 



The Diamond Head breccia contains a considerable num- 

 ber of extinct species. Dune sand, interbedded with land- 

 shell breccia, where the section has been fully exposed in the 

 sand quarry along the road, contains only recent marine shells. 

 I conclude therefore that the Diamond Head and Punch- 

 bowl land-shell deposits are Pleistocene, not Pliocene. A cer- 

 tain proportion of special species would naturally be ex- 

 pected in a region of such intense local endemicity as Oahu. 

 They are not of themselves an indication of age. 



Whether any fossiliferous deposits older than Pleistocene 

 will be found on Oahu is doubtful. There is a possibility 

 of inland deposits, but if the movement of the island has 

 been mainly downward, as I believe, there is little probability 

 that marine Tertiary beds will be found near the surface. 



Recent Climatic change. 



That there has been a change from more humid to dryer 

 climate in many districts of all the islands, if not known by 

 historic evidences would be demonstrated by the restriction 

 of most land snails to higher levels than formerly occupied. 

 Sixty years ago the Achatiuellas were found in abundance 

 at half the elevations now inhabited by them. Still earlier 

 forest shells lived within a few feet of the present sea level, as 

 the Kailua and Kahuku deposits show. Forest shells, 

 Amastra and others, are found in many of the low deposits, 

 and it is obvious that the Pleistocene forests extended nearly 

 or quite to the sea on the northern and western coasts of 

 both Oahu and Molokai. The changes within the last cen- 

 tury are held to be due to deforestation by cattle, which by 

 destroying the underbrush cause the dessication of the forest 

 humus, and prevent reproduction of the native trees. In 

 Laiiai the wild goats have almost, and in Kahoolawe have 

 totally, completed the destruction of native forests. With 



