Apeil 13, 1900.] 



SCIENCE. 



677 



west of Guam made by the Challenger. 

 We obtained, about 100 miles southeast of 

 Guam, a deptli of 4813 fathoms, a depth 

 surpassed only, if I am not in error, by 

 three soundings made by the Penguin in 

 the deep trough extending from Tonga to 

 the Kermadecs. 



I was very much surprised, in approach- 

 ing Guam from the eastward, to find that 

 the island was not wholly volcanic, but 

 that the northern half has been built up of 

 elevated coralliferous limestone. The ver- 

 tical cliffs bordering the eastern face rise 

 from a height of 100 to 250 or 300 feet at 

 the northern extremity, and resemble in 

 a way similar islands in the Paumotus 

 (Makatea), Nine, Eua, Vavau and others 

 in the Fijis which had made their cliffs a 

 familiar feature in our explorations. In 

 fact, outside of Viti Levu and Vanua Levu, 

 this is the largest island known to me where 

 we find a combination of volcanic rocks and 

 of elevated coralliferous limestone. The 

 massif forming the southern half of the 

 island is volcanic, and the highest ridge, 

 rising to about 1000 feet, runs parallel to 

 the west coast, the longest slope being to- 

 ward the east. 



This volcanic mass has burst through the 

 limestone near Agana, and the outer west- 

 ern extension of the coralliferous limestone 

 exists only in the shape of a few spurs run- 

 ning out from the volcanic mass, the larg- 

 est of which are those forming the port of 

 San Luis d'Apra. These' spurs are sepa- 

 rated by lower ridges of volcanic rocks ex- 

 tending to the sea from the main central 

 mass. To the north of AgaiJa the lime- 

 stone forms an immense irregular mesa, cut 

 by deep crevasses, full of pot-holes and 

 sinks, rising gradually westward to a height 

 of 350 or 400 feet. Near the northern ex- 

 tremity of the island a volcanic mass, Mt. 

 Santa Eosa, has burst through the limestone 

 and rises about 150 feet above the general 

 level of that part of the island. The shore 



stratification of the bluffs is much distorted 

 in the vicinity of that volcanic outburst. 



We left Guam in time to reach Rota by 

 day, and found that this island is a mass of 

 elevated coralliferous limestone, the highest 

 clifis of which reach a height of 800 feet. 

 Perhaps in none of the elevated islands 

 have we been able to observe the terraces 

 of submarine elevation as well as at Eota, 

 especially in the small knob at the south- 

 west point of the peninsula separating So- 

 sanlagh and Sosanjaya bays, which itself 

 is also terraced ; no less than seven distinct 

 terraces could be traced. There was no 

 sign of any volcanic outburst except at the 

 northwest point of the island, where both 

 the character of the slope and of the veg- 

 etation would seem to indicate volcanic 

 structure. 



It is quite probable that others of the 

 Ladrones, like Saipan, and the islands to 

 the south, are composed in part at least of 

 elevated limestone judging from the hydro- 

 graphic charts and the sketches which ac- 

 company them. On many of the northern 

 Ladrones there are active volcanoes, so that 

 it is very possible that the volcanic outbursts 

 which have pushed through the limestone, 

 or have elevated parts of the islands of the 

 group, are of comparatively recent date. 



During the last part of our cruise, from 

 Suva to Guam, the unfavorable weather 

 greatly interfei'cd with our deep-sea and 

 pelagic work ; in fact, with the exception 

 of the soundings made to develop as far as 

 practicable the depths in the regions of the 

 various coral-reef groups we visited, we 

 abandoned all idea of carrying out the 

 deep-sea and pelagic work planned for the 

 district between the Gilbert and Miarshall 

 and Caroline groups. To our great disap- 

 pointment hardly any marine work could 

 be accomplished, and our investigations 

 were limited almost entirely to the study of 

 the coral reefs of the regions passed through. 



After Mr. Townsend's departure. Dr. 



