GEOLOGY. 837 



he perceived a squall abaft the beam, but this turned out to be a warm mist, 

 or steam. Where the mist was, the sea boiled or surged up from the bottom. 

 It was in. those seas that the island of Salerina appeared in 1811. 



ON CERTAIN CONNECTING POINTS BETWEEN LUNAR AND TERRES- 

 TRIAL VOLCANOES. 



The following paper was recently read before the Royal Astronomical 

 Society, by Prof. C. Piazzi Smith : 



In a recent publication of our Society the upper parts of Teneriffe were 

 described as a most moon-like region. The expression is not a little de- 

 scriptive; and why? Because, at those elevations the air is thin and trans- 

 parent; no cloud floats therein during a large part of the year; vegetation is 

 reduced to a minimum; sharp jagged rocks rear their naked forms around, 

 brilliantly, and even blindingly illumined by the intense rays of an un- 

 dimmed sun on one side, while they throw on the other shades as remarkable 

 for their darkness ; and, finally, all those rocks, plains, and slopes, are thor- 

 oughly and purely volcanic. Every astronomer will at once understand and 

 allow the connection, but would yet do unwisely were he to overlook the opin- 

 ions of several eminent geologists, who affirm that the telescopic features 

 made out on the lunar surface are not volcanic at all. However positively 

 this view is maintained in conversation, I have not yet been fortunate enough 

 to meet in print with anything that could, with due respect to geologists of 

 standing, be considered a full exposition of their reasons. Rather, then, 

 than attempt to discuss opinions evidently weak and confessedly imperfect, 

 and without entering into the extensive subject of volcanoes generally 

 though for their natural development and proper action, pur et simple, the 

 moon might perhaps be shown to be a fitter region than the earth I will 

 at present merely bring forward some few facts, equally acceptable, I trust, 

 as facts to either party, and calculated to supply, in some measure, a short 

 link in that large gap which intervenes between the methods of observation 

 hitherto employed on lunar or terrestrial volcanoes, real or imaginary. An 

 immense difference of this sort must always prevail; for whereas actual 

 eruptions, and chemical analysis of the materials erupted, are the most 

 powerful of proofs for earthly craters, we can never hope to employ them in 

 the moon. There are naught but extinct volcanoes, so distant from us, too, 

 that rare indeed it is to find a man who can completely realize what he sees of 

 figure and surface with the telescope, so as to form in his mind as rational 

 an idea of them as he does of an earthly mountain that he has actually 

 walked over. To approximate these respective methods of research, and in 

 that way eliminate their peculiar sources of error, we may evidently, with 

 much advantage, leave the active volcanoes of the earth (say Vesuvius) 

 where the fire and fiery smoke, and devastations of the last or present erup- 

 tion, force themselves too prominently on the eyes and nerves of all behold- 

 ers, and turn rather to some extinct specimen, where we may contemplate 

 the traces of successive eruptions during myriads of years, and the last of 

 them as impassively as the first; always provided that such instance be not 

 overlaid by any geological changes consequent on our dense and watery 

 atmosphere, and that its features can be viewed from such heights and dis- 

 tances as in the naked eye to subtend something like the same angles that 

 those of the moon do in the telescope. Had we to search over the whole 

 breadth of the earth for such an example, we could hardly find a better 



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