394 COSMOS. 



tior of Captain "Wilkes was based on investigations of twenty- 

 eight days' duration, mention is made of falls of snow with a 

 degree of cold from 23 to 17^- F. above zero, and of single 

 patches of snow, which could be distinguished with the aid 

 of the telescope at the summit of the volcano, but nothing 

 is ever said of perpetual snow. 90 I have already observed in 

 a former part of this work that the Mouna Loa (13,758 feet) 

 and the Mouna Kea (13,950 feet) are respectively more than 

 1000 and 821 feet lower than the lowest limit of perpetual 

 snow as found by me in the continental mountains of Mexico 

 under 19 4 latitude. On a small island the line of perpetual 

 snow should lie somewhat lower, on account of the less ele- 

 vated temperature of the lower strata of air in the hottest 

 season of the tropical zone, and on account of the greater 

 quantity of water held in solution in the upper atmosphere. 



The volcanoes of Tafoa* and Amargura* 1 in the Tonga- 

 group are both active, and the latter had a considerable 

 eruption of lava on the 9th of July 1847. 91 It is extremely 

 remarkable and is in entire accordance with the stories of 

 the coral animals avoiding the shores of volcanoes either 

 at the time or shortly before in a state of ignition, that the 

 Tonga islands of Tafoa and the cone of Kao, which abound 

 in coral-reefs are entirely destitute of those creatures. 92 



Next follow the volcanoes of Tanna* and Ambrym,* the 

 latter westward of Mallicollo in the archipelago of the New 

 Hebrides. The volcano of Tanna, first described by Rein- 

 hold Forster, was found in a full state of eruption on Cook's 

 discovery of the island in 1774. It has since remained con- 

 stantly active. Its height being only 458 feet, it is one of 

 the lowest fire-emitting cones, along with the volcano of 

 Mendana, hereafter to be noticed, and the Japanese volcano 

 of Kosima. There is a great, quantity of pumice on Mall- 

 icollo. 



Matthew's Rock ; * a very small smoking rock-island, 

 about 1183 feet high, the eruption of which was observed 



90 Wilkes, pp. 114, 140, and 157; Dana, p. 221. From the per- 

 petual transmutation of the r and the I, Mauna Loa is often written 

 Koa, and Kilauea, Kirauea. 



91 Dana, pp. 25 and 138. 



92 Dana, Geology of the U. States Exploring Exped., p. 138. (See 

 Darwin, Structure of Coral Reefs, p. 60). 



