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WONDERS OF GEOLOGY. Vol. I. 



up; while from the foot of this lunar mountain, streams of lava 

 diverge in different directions, to the distance of six hundred miles. 

 The longest known current of modern lava on the earth is in Iceland, 

 and extends sixty miles ; but the volcanoes in that island bear no pro- 

 portion to those of the moon in magnitude. — Mr. BakewelL 



B. Page 77. — The Lake of the Solfatara. — " Its temperature 

 was, in the winter, in the warmest parts, above 80 deg. of Fahrenheit, 

 and it appears to be pretty constant ; for I have found it to differ a few 

 degrees only, in January, March, May, and the beginning of June ; 

 being therefore nearly twenty degrees above the mean temperature of 

 the atmosphere, it must be supplied with heat from a subterraneous 

 source. Kircher has detailed in his Mundus Subterraneus various 

 wonders respecting this lake, most of which are unfounded ; such as 

 that it is unfathomable, that it has at the bottom the heat of boiling 

 water, and that floating islands rise from the gulf. It must certainly 

 be very difficult, or even impossible to fathom a source which rises 

 with so much violence from a subterraneous excavation j and at a time 

 when chemistry had made small progress, it was easy to mistake the 

 disengagement of carbonic acid for an actual ebullition. The floating 

 islands are real, but neither the Jesuit nor any of the writers who have 

 since described this lake, have had a correct idea of their origin, which 

 is exceedingly curious. The high temperature of this water, and the 

 quantity of carbonic acid that it contains, render it peculiarly fitted to 

 afford a pabulum or nourishment to vegetable life ; the banks of tra- 

 vertine are every where covered with reeds, lichens, confervae, and 

 various kinds of aquatic vegetables. At the same time that the 

 process of vegetable life is going on, the crystallization of the cal- 

 careous matter which is every where deposited, in consequence of the 

 escape of carbonic acid, likewise proceeds, and gives a constant milki- 

 ness to what from its tint would otherwise be a blue fluid. So rapid 

 is the vegetation, owing to the decomposition of the carbonic acid, 

 that even in winter, masses of confervae and lichens, mixed with 

 deposited travertine, are constantly detached by the currents of water 

 from the bank, and float down the stream; which being a considerable 

 river, is never without many of these small islands on its surface. 

 They are sometimes only a few inches in size, and composed merely of 

 dark green confervae, or purple or yellow lichens; but, occasionally, 

 are even several feet in diameter, and contain seeds and various species 

 of common water-plants, which are usually more or less incrusted with 

 marble. There is, I believe, no place in the world where there is a 



