SALT LAKE GROUP OF CRATERS 39 



over the surface as far as to the railroad, which in certain situations rest 

 on a cushion of tuff, looking just as if they had fallen from the sky on 

 soft mud. Figure 1, plate 6, shows the appearance of such an indentation 

 with its boulder, and others appear in the distance. The largest of the 

 fragments observed in the neighborhood is 8 feet square and 4 feet high. 

 Nearer the lake large stones are imbedded in the tuff, which wraps them 

 in concentric layers, and therefore it is probable that all of them orig- 

 inally occupied similar positions. 



Aliamanu is on the north side of Salt lake, and has smaller dimen- 

 sions, while its base is elevated 50 feet above the sea, and in the wet 

 season may show a large pond of water. More exact measurements make 

 Aliapakai 3,000 and 4,000 feet in the two diameters, and Aliamanu 1,300 

 and 2,000 feet. The highest part of the circular wall, Leilono, on the 

 north side of Aliamanu is 486 feet above tide water. On much of its bared 

 extent may be seen a conspicuous white coating of calcium carbonate, 

 with limestone fragments and the other constituents mentioned as exist- 

 ing in the Salt Lake tuff. The government road on the east side of these 

 craters has been cut through solid basalt and clinkers that belong to the 

 Koolau range, as also many pebbles and cobbles containing a profusion 

 of crystals of labradorite in the bed of the stream, a branch of Moanalua. 

 Both of the Salt Lake craters exhibit well the usual double quaquaversal 

 stratification, and the dividing rim belongs to both. 



Mr Green regards the Salt Lake craters as the oldest of the secondary 

 cones about Honolulu, because of the considerable erosion that is indi- 

 cated, and this may be well seen in the view from the Pearl City neigh- 

 borhood. On looking at a large scale map it will be noted that the 

 more western branch of Moanalua stream was dammed up by the Salt 

 Lake outflows, and consequently the water has been forced to cut its way 

 through them, excavating a can} r on more than a hundred feet deep. 

 Portions of the tuff now lie on the eastern bank, resting on the Koolau 

 basalt. The part deeply excavated is not quite a mile in length. This 

 western branch joins the eastern above Moanalua station, and the en- 

 larged stream continues to the sea through a broad plain, in the direc- 

 tion of the latter valle}^. The low plain is half a mile wide, now occu- 

 pied by rice fields, and its whole area was once occupied by the tuff, 

 because it constitutes the promontory on the east side. The upper part 

 consists of large rounded pebbles underlaid by an earth exhibiting fossil 

 plants on the road east of the Pacific guano fertilizer establishment. 



Professor A. B. Lyons calls attention to a fine grained sandstone which 

 originated in connection with the building up of the Salt Lake craters. 

 The material was brought down the Moanalua stream, consisting per- 

 haps of fine particles blown out of the crater, which were carried by 



VI— Bull. Geol. Soc. Am., Vol. 11, 189«J 



