Vol. I] WILLIAMS— BUTTERFLIES AND HAWK-MOTHS 293 



the reader an idea of their character (Plate XXI). The upper 

 or humid portion of the island (500 feet and up) is very diffi- 

 cult of access owing to the dense tangle of vines and scarcity of 

 water. The island was not explored above 1000 feet altitude, 

 therefore the character of the vegetation above about 1400 feet 

 was not satisfactorily ascertained, but by means of observations 

 through binoculars and by observing the slopes and summits of 

 other high and more accessible islands of the group, a doubtful 

 idea of the "Brown Zone" was obtained.^ Indefatigable Island 

 is about twenty-five miles in diameter and nearly circular in 

 outline, and is situated a little south of the center of the main 

 Archipelago. Its height is estimated at a little over 2200 feet, 

 but it appears fully 3000 feet high. The slope from shore to 

 summit is very gradual and comparatively uniform, and the 

 lower or arid area of much greater extent than the more 

 elevated humid regions. The summit of Indefatigable Island 

 probably contains a large crater. This portion of the island is 

 very commonly enveloped in clouds. The two well-defined life 

 areas, the arid and the humid, can each be subdivided into 

 regions of a less distinct character, and the former are connected 

 with each other by a species of transition or "Big Tree" zone 

 which has a lighter green appearance than the "Green" zone 

 above it. 



Commencing at the shore line, we find the "Arid" zone 

 skirted by a littoral flora composed largely of such trees as 

 Rhisophora mangle/' Avicennia officinalis. Hibiscus tiliaceus, 

 the poisonous Hippomane mancinella, and the stout creeping 

 vine, Ipomoea pes-caprcB. Usually the above mentioned plants 

 do not occur inland any distance, except sometimes about bodies 

 of water. 



Proceeding towards the interior of the island, one passes 

 through nearly two miles of rough desert-like country where 

 there is but little soil but an abundance of lava. Here the two 

 genera of Cactacecs {Cereus and Opuntia), Croton scouleri, 



^ Indefatigable Island has been selected for the illustration of the zones on account 

 of the well-defined appearance of the latter there. It must be borne in mind that 

 elsewhere in the Archipelago, they are on the whole, far less distinct. 



^ I am indebted to Mr. Alban Stewart, botanist to the expedition, for a number of 

 the botanical names given in this paper. In the proceedings of the California Academy 

 of Sciences, Vol. I, 4th Ser., pp. 206-211, Mr. Stewart gives the botanical regions and 

 zonal elevations more in detail. 



