NOTES ON THE TERTIARY GEOLOGY 57 



tuff by rain. Professor Lyons writes that he has observed terraces, ap- 

 parently of marine origin, on the coast side of the Pali 100 feet above 

 tidewater. Brigham and Dutton in their writings agree as to the exist- 

 ence of a depression of the land somewhere about 200 feet at this epoch. 

 Some one asks, Could not the elevation of these organisms have been 

 effected b}^ an earthquake wave ? 



17. Elevation to the present level. Accumulation of dunes. 



Notes on the Tertiary Geology of Oahu* by W. H. Dall 



During a visit to Honolulu in August and September, 1899, I exam- 

 ined with much interest the scanty fossiliferous strata which exist in 

 that vicinity. 



Near the eastern extreme of the island are quarries of calcareous rock 

 from which road metal is obtained. These beds contain stratified layers 

 partly of rnore or less consolidated coral sand interstratified with brec- 

 ciated tuffaceous material, apparently deposited in water, the interstices 

 filled with fine marl containing small species of Helicina and Achati- 

 nellidse of the small terrestrial types, such as Amastra and Auriculella. 

 Here and there were small lenticular masses of fine blackish sand with 

 many granules of olivine. 



Ascending to a more or less denuded surface largely corresponding to 

 a layer of volcanic rock which forms the natural surface of the ground 

 above the quarries, here and there patches of calcareous rock remained 

 in depressions in the lava, containing thoroughly fossilized marine, 

 shells of many genera, of which the most conspicuous were the solid 

 shells of Conus and Purpura, tropical types of the Indo-Pacific fauna, 

 but, so far as my observation went, not at present represented on the 

 adjacent beaches. This horizon corresponds to that of the basal lime- 

 stones of Diamond head, farther east. 



Diamond head, the conspicuous hill at the southeastern extreme of 

 the island, is isolated and considerably denuded, but exhibits numerous 

 good sections, especially on the seaward face near its base. It is com- 

 posed of horizontal layers of tuff, interstratified with thin layers of cal- 

 careous sand, the lime from which, leached out by the rain, is redepos- 

 ited in a thin superficial crust of a brilliant white, giving the effect, 

 among the sparse arid vegetation, of a thin layer of snow. The strata 

 of the Head have not the " onion peel " aspect of layers of successive 

 subaerial eruptions, but are strictly horizontal and have every aspect of 

 having been deposited in water. Occasional somewhat thicker layers 

 of sand show " wave structure " in their fluctuated lines. 



* Printed by permission of the Director of the U. S. Geological Survey. 



