Chap. XV.] INSECT.S AT MOUNTAIN TOPS. 331 



and the remainder white ; the decomposition not havino- 

 reached as yet through the whole. 



Jets of hot steam issued in many places from fissures. 

 Around the mouths of these were growing gelatinous masses 

 formed by lowly organised alga? closely similar in appearance 

 to those found growing around the mouths of hot springs in 

 the Azores.* Here, however, there was no water issuing, the 

 only moisture being supplied by the condensation of the steam. 

 There was no accumulation of water, but drops of moisture 

 hung on the sides of the fissures. 



In some places the gelatinous alga;, and a white mineral 

 incrustation, formed alternate layers coating the mouths of the 

 fissures. The steam on issuing within the fissure had a tem- 

 perature of 250° F. ; and where the crust of algae was flourishing 

 the thermometer showed 140° F. The steam had a strongly 

 acid and sulphurous smell. 



On the summit of the mountain, where the ground is cool. 

 Fern, a Sedge, and a Melastomaceous Plant grow. Besides 

 these, I found another flowering plant, growing in a crack in 

 the midst of a strongly sulphureous smoke which issued con- 

 stantly from it. The thermometer when laid on the surface of 

 the ground where this plant was growing showed a temperature 

 of 100° F. ; and at a depth of one and a half feet below it the 

 soil about the fissure had a temperature of 220° F. 



At the summit of the mountain were numerous flying insects 

 of various kinds, although there was nothing for them to feed 

 upon, and large numbers of them lay dead in the cracks, killed 

 by the poisonous volcanic vapours. So numerous were they 

 that the Swallows had come up to the top of the mountain to 

 feed on them. 



I noticed similarly large numbers of insects at the summit 

 of the volcano of Ternate, at an altitude of more than 5,000 

 feet. Insects are commonly to be seen being carried along 

 before the wind in successive efforts of flight. No doubt they 

 are blown up to the tops of these mountains, having towards 

 the summits no vegetation to hold on to. The winds pressing 

 against the mountains form currents up their slopes ; and in 

 the case of volcanoes, which are heated at the summits, no 

 doubt there is a constant upward draught towards their tops, 

 caused by the ascending column of hot air. 



I dwell on the accumulation of insects at the tops of these 

 mountains, because when blown off' into the free air from these 

 great elevations by heavy winds, as no doubt they often are, 

 the insects are likely to fly and drift before the wind to very 

 long distances, and thus be aided in colonizing far-off" islands. 



'■'' See page 32. 



