544 



PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 2, 



to give no credit to the well-attested frequent and great changes 

 of form in the cone and crater of that mountain, many even 

 within memory of man, and to which I have already referred — 

 changes, the earlier of which are admirably delineated and de- 

 scribed in the great work of Sir William Hamilton, who himself 

 witnessed many of them between 1768 and 1800, during which long 

 period of thirty-two years he resided at Naples and continually 

 watched the volcano (see figs. 22 and 23). Coming to a later period, 

 the upheavalists do not seem to be aware that for some years previous 

 to 1822 Yesuvius had no crater at all, but showed on its truncated 

 summit a rough platform upon which several parasitic cones were 

 occasionally thrown up, and subsequently destroyed by minor erup- 

 tions, while streams of lava flowed from them almost continually 

 down the slope of the cone and hardened there. They do not seem 

 at all aware that the explosions of 1822 blew off the summit of the 

 cone with aU its excrescences, lowering its absolute height by some 

 600 or 800 feet *, and replacing the solid platform by a crater a mile 

 in diameter and a thousand feet deep, which vast cavity was Tvithin 

 a very few years filled again by subsequent eruptions from the 

 bottom, and has been again nearly emptied and re -filled in a similar 

 manner more than once f. (See fig. 24.) In the face of these well- 

 known facts we have M. de Humboldt endorsing the strange dictum 

 of de Buch, that Yesuvius has not changed at all in height or 



Fig. 24. — Ideal Section of Vesuvius and Somma before and after the 



eruption of 1822. 



The fainter lines represent the portion removed by the eruption. 



bulk since the year 79 of our era ; and gravely attributing recorded 

 differences in its height either to incorrect measurements only, or 

 internal elevation en masse — that is, renewed upheaval of the entire 

 cone i. 



It is singular that the geologists of the last century, Hamilton, 

 Breislak, and Spallanzani, should have held views respecting the 

 action of volcanos so much more accordant with the truth than 



* Reducing it from 4200 feet to 3400 feet above the sea. — Forbes, 

 t See mj paper on Craters, &c., Proc. of Greol. Soc, vol. xiv. p. 335, 



- - -- Kosmos, iv. p. 346. 



I Humboldt, Tableaux de la Nature : Paris, 1829. 



