VIEWS OF VARIOUS GEOLOGISTS 477 



have come from the only possible source, direct or indirect, namely, the sea 

 sediments and beach sand. There seemed to me to be in that cone altogether 

 too much lime to be derived merely from the crumbling of the walls of the 

 vent after the latter became fully established. 



"I think the marine fossils I got around Diamond head and at Pearl har- 

 bor were indubitably Pliocene, at least they are not (so far as yet known) 

 represented in the present fauna. Yet here we are met by the difficulty that 

 the Hawaiian marine shells are very imperfectly known. Still, there can be 

 no doubt that some of those I found are extinct ; it is only the proportion 

 which for the present must remain uncertain. As for the land shells in the 

 rock at the quarry north of the road, before we turn the corner of the island. 

 I did suggest that they might be Pliocene, but without dogmatism, as a de- 

 cision on this point must depend on an expert and minute knowledge of the 

 species, which I can not claim. They seemed to me wind blown, and the 

 limestone, in which they were, to be subaerially deposited and solidified by 

 the percolation of rainwater. This is a process which might continue indefi- 

 nitely, the shells in upper layers being much younger, geologically, than those 

 below, and much would depend on an exact stratigraphic correlation of the 

 fossils. I found no Amastras ; the others you mention are all old types which 

 might go back to the Eocene without violating precedent. I should be much 

 interested to see your series." . . . 



Observations made in 1905 



Keturning now to the discussion of the observations made in 1905, it 

 is needful to recall the general structure of Oahu. It has two ranges of 

 basalt parallel to each other, separated by a sloping plain. The ranges 

 are Kaala and Waianae on the southwest and Koolauloa and Koolaupoko 

 on the northeast, the last being 37 miles long. Kaala is the oldest and is 

 supposed to have been the only dry land for a long period. Koolau came 

 into being later, as its discharges have covered up the eroded eastern out- 

 line of Kaala. Each basaltic mass represents an independent center of 

 volcanic action, whether originating at the bottom of the ocean or arising 

 from low Tertiary land. The profuse rainfall due to the impingement 

 of the moist vapors brought by the trade winds on the highlands, has ex- 

 cavated numerous canyons and amphitheaters on both sides of Koolau, 

 but with much greater erosion on the most exposed portion, looking 

 northeasterly. For part of the way the erosion has reached the center of 

 the range, where the sheets are disposed in an anticlinal fashion. On the 

 opposite side the canyons, at first conspicuous, east of Honolulu are less 

 prominent, and for a time it was believed that there was a gradual slope 

 from the crest of the range to the valleys leading both northeast and 

 southwest from the highest point of the plain. Now that the region has 

 been better explored, it is found that there are deeply incised canyons 

 along the whole southwestern slope of Koolau in the upper reaches. The 



