30 c. H. E1ITCHCOCK — GEOLOGY OF OAHU 



north of Barbers Point (Laeloa) light-house the best quality of the sand- 

 stone is well developed, and was used in the erection of the Saint An- 

 drews English cathedral. Agassiz speaks of this material as a " massive 

 coral pavement sandstone/' 



There are three varieties of material at this locality : At the base, the 

 underlying rough reef loosely put together, a sandy limestone, and above 

 all, the compact pavement sandstone, capable of affording a good polish. 

 The total height is about 1G feet. This compact rock has been utilized 

 also in the manufacture of quicklime. Tt is a good place in which to 

 observe the manufacture of the sandstones, for shells and corals are 

 strewn over the beach in all stages from the live animal to worn cobbles, 

 pebbles, sand, and firm rock. Crystals of calcite are frequently seen in 

 the consolidated rock. 



Proceeding northerly, Professor Alexander reports a ledge of coral 79 

 feet above the sea, at Kahe, and 730 feet distant from the water, south 

 of Pun o Hulu, he mentions another ledge 56 feet above the sea and a 

 quarter of a mile inland ; also on the south side of Lualualei, 20 feet 

 high. At the south end of the ridge called Mailiilii, the limestone reaches 

 the height of 81 feet ; at other localities on this coast I have observed 

 limited areas of the same substance more or less elevated. 



The plain of Waialua shows many outcrops of the reef; Kahuku, the 

 extreme northern point of Oahu, is the most interesting locality. The 

 Koolau highlands ends in a bluff nearly 2 miles back from the extreme 

 point, rising to a hundred feet or more from a fiat plain. This bluff con- 

 sists of coral rock up to 60 feet, capped by blown calcareous sand now 

 firmly consolidated, which may extend inland to a height of 250 feet. 

 Plate 4 shows both these varieties of limestone : First, the reef up to 60 

 feet, at the line just above the principal cave opening; second, the con- 

 solidated sandstone higher up. Large blocks of the latter material have 

 fallen from the cliff on all sides, and similar masses in the edge of the 

 ocean adjacent are large enough to constitute islands, delineated on maps 

 of a large scale. At various localities in the neighborhood I found corals 

 and shells in the underlying limestone, but nothing in the sandstone 

 above, save perhaps a shell brought by a hermit-crab. Professor Dana 

 has given a very effective figure on page 302 of his " Characteristics of 

 Volcanoes," illustrating this plane between the two limestones. Nowhere 

 on the windward side of the island do the winds blow more vigorously 

 than here, and hence the explanation of the great altitude attained by 

 this blown consolidated sand. For 5 miles southeasterly, to even be- 

 yond Laie, the coral plain is quite extensive. Knobs of the consolidated 

 sand with inclined strata rise to the height of 35 feet, and sometimes 

 suggest an assemblage of kames. Several other localities of coral mate- 



