146 BULLETIN OF THE 



East Range also drains into the lagoon. Pearl River Lagoon is the 

 remnant of an old entrance like that of Honolulu, when the old shore 

 line was just inside the great plain of coral rock extending to the west- 

 ward of the lagoon as far as Kalaeloa, the shore line being then its inner 

 line. 



The very characteristic bedded coral sand rock so common along the 

 shores of the Florida Keys and of the Tortugas is not common on the 

 southern reef of the island of Oahu. It is replaced by the formation 

 of the massive coral sandstone pavement described above. This, how- 

 ever, is, as with the finer-grained sandstone, often broken into large rec- 

 tangular slabs, which in their turn have been uplifted by seas unusually 

 heavy, and thrown back on the more exposed beaches. 



A very characteristic formation found only on the shores of volcanic 

 islands fringed with corals is the peculiar pudding-stone formed of 

 rounded and water-worn pebbles of volcanic origin, derived from adjoin- 

 ing basaltic rocks dipping into the sea. These pebbles are cemented 

 together by coral limestone, sometimes only a single stone in a mass of 

 white coral or the cementing matei'ial merely filling the interstices and 

 barely holding the pebbles together. So that we have all possible grada- 

 tions between a compact coral sandstone, with here and there a pebble 

 enclosed, and loose friable and poorly cemented rock. There is no local- 

 ity on Oahu where the process of formation of this conglomerate can be 

 better seen than at the very eastern extremity of the Honolulu reef, at 

 the foot of Diamond Head. This pudding-stone has already been de- 

 scribed by Dana, who also called attention to the fact that some of the 

 pebbles are evenly covered with a very thin incrustation of lime, look- 

 ing as if they had been dipped in milk. The lime in solution is also fre- 

 quently deposited in the seams of the volcanic rocks, which then resemble 

 irregular dikes, and their cavities when filled with limestone change 

 cellular lava into a sort of amygdaloid. Perhaps no better evidence of 

 the amount of carbonate of lime taken up by sea-water can be given 

 than that furnished by this constant deposition of lime from evaporation 

 of apparently pure sea-water. 



The Sandwich Islands are peculiarly placed in the track of the trade 

 winds, so that they all present a dry and a moist side. One side is 

 rediant with verdure, and its mountain slopes are furrowed by innumer- 

 able streams, cutting deep valleys on the weather face. The streams 

 become powerful torrents during the rainy season, and pour an immense 

 amount of fresh water into the sea, — so large a quantity as materially to 

 influence the growth of coral reefs on that side. An examination of the 



