HENSHAW SE.MI-FOSSIL SHELLS IN HAMAKUA DLSTRICT, HAWAIL 59 



of various species occur in extraordinar)- abundance. In the case of the 

 deposits in question it need be assumed only that an unusual mortaUty 

 occurred simultaneously among the shells of a ceitain district, such as in- 

 variably follows a forest fire, and that there shortly ensued a deluge that 

 washed the dead shells into their present abiding place. The gentle slope 

 of the land around the deposits in both localities entirely favours this 

 supposition. 



That the shells forming the deposits cannot have been carried from any 

 considerable distance is proven by the condition of vast numbers of the fossil 

 jSurrineas, many of which when cleaned from dirt might almost seem to have 

 been alive but yesterday. 'i"he steeper slopes of Mauna Kea are not more 

 than four miles to the south west of the localities in question, bat the 

 general lay of the land, and the fact that a wdl defined ridge intervenes, 

 forbids the assumption that the shells originated on the distant slopes of 

 the mountain and were transported to their present position, even if the 

 condition of the shells themselves did not prove the contrary. 



The humus above the fossils in both localities is perfectly hcjmogeneous, 

 and the general absence in it of shells is especially noteworthy, indicating 

 to the writer that the destruction of the fossils resulted from the destruction 

 of the forest, or at any rate occurred at about the same time, the locality 

 then ceasing, except in a small way, to be a shell producing one. Had the 

 forest persisted after the deposition of the fossils, the humus overlying the 

 fossils would contain evidence of the fact in the presence of shells, either of 

 the same or of other species, which would have re-populated the forest. 

 The grass in the neighbourhood still shelters a few small species like 

 Leidachatina and Tornafrllina, and it is probable that the genera Pupa 

 and Jlirrorij.'ifi.-^ are still represented here and there although none rewarded 

 our search. Specimens of Succiwa /iV>u(cii^/-'<, Sykes, were found hard by, 

 and the Acliatindla ph!j><(i, Newc, also is found in the neigbourhood. 

 Dead shells of the above species were found on the surface of the ground 

 and perhaps an inch or so below, but further down they seem to be entirely 

 wanting. 



In connection with the question of the age of the deposits, it is to be 

 said that the humus everywhere presents the appearance of having been laid 

 down by the natural decay and deposit of the tropical vegetation. Never- 

 theless, I cannot think that such is the case, but believe that most of the 

 humus above the shells must have been washed into place subsequent to 

 the deposit of the shells. The deposition of a foot of humus by natural 

 decay, even in a luxuriant semi-tropical forest, must require several hundred 

 years, and the condition of the shells generally would seem to negative any 

 such age. It is true that in a few places the shells have been reduced to 

 lime, all semblance of their form and character having disappeared. On the 

 other hand, thousands of the frail Surcineas, TornaM/tnaf, and Pupa^, as 

 well as many of the more substantial species like the A)nasfrat< and the 

 Arhafine//as are but slightly affected by time. 



