THE TERTIARY LIMESTONES 479 



the suggestions of Dr Alexander Agassiz* as to the limestones of the Fiji 

 islands, with the concurrent determination of age derived from a study 

 of the mollusca of the limestones by Dr W. H. Dall, compared with the 

 existing fauna. 



It was my good fortune to be able to glance at these Fijian deposits 

 while studying the Hawaiian phenomena, and to be satisfied of the essen- 

 tial unity in age of these Pacific groups of islands. Hence in my paper on 

 the geology of Oahuf I considered the Pearl River series to be of Tertiary 

 age, consisting of marine deposits, decayed rock, limestones, clays, pebbly 

 layers, secondary volcanic products, ashes, and solid basalts fully 1,000 

 feet thick. Very fortunately Doctor Dall visited Oahu just as I was 

 leaving and made comparisons of the shells found in the earthy deposits 

 with those now living. Some species of Conus, Purpura, Chama, and 

 Ostraea are apparently extinct. Hence it is as proper to call the Hawaiian 

 beds Pliocene as those of Fiji. Doctor Dallas views on this subject are 

 embodied in a letter published elsewhere in this communication. 



The Pliocene area of Oahu coincides very nearly with the lowland 

 tracts utilized for the cultivation of the sugar-cane and sisal, from Bar- 

 bers point to Koko head. Smaller patches appear at Waianae, Waialua, 

 at the Kahuku plantation, Laie, and other places on the northeast coast. 

 This distribution suggests the existence of a large low island or shoal prior 

 to the ejection of one or both of the great basalt ranges. If so, why was 

 there not also a submarine Pliocene or older foundation for the whole 

 archipelago ? This would not render it necessary to abandon the notion, 

 so constantly repeated, that the beginnings of land correspond to sub- 

 marine volcanic eruptions. 



Limestone is common over the whole plain between Ewa and Koko 

 head, not merely at the surface, but in the artesian borings.^ A locality 

 of interest is just northeast of Diamond head, where Doctor Dall found 

 fossils referable to the Pliocene. I went over the ground last summer 

 under the guidance of Professor Edgar Wood of Honolulu, who showed 

 me the ledges from which Doctor Dall obtained his specimens. Proceed- 

 ing farther east, the promontory of Kupikipikio was found to consist of 

 basalt, both in dikes and as a boss. 



The dikes cut the limestone as illustrated in plate 61, figure 2, and 

 plate 62, figure 1. Figure 2, plate 61, shows a black ledge of basalt next 

 to the water, with limestone behind it higher up. The black stones to the 



* Amer. Jour. Sci., IV, vol. vi, p. 165. 



|Pp. 31-34. 



t Bull. Geol. Soc. Am., vol. 11, p. 28 et seq, 



