332 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 23> 



falling inwards. But such a supposition is, in the present state of 

 our knowledge, purely conjectural, and unwarranted, if, as I have 

 endeavoured to show, the ordinary phsenomena of eruption suffice to 

 account for the formation of the largest known craters. If it is to 

 be resorted to in any case, it would be, perhaps, in that of the very 

 small pit-craters, occasionally met with in volcanic districts, such as 

 the Gour de Tazana, and the lakes Pavin, DuBouchet, and Servieres 

 in Central France. But even these show marks of explosive eruption 

 in the scoriae sprinkled around their banks. And the occurrence of 

 even a single scoria is certain proof of some explosions having taken 

 place from a body of liquid lava beneath ; though, as I have said, 

 this may have been accompanied or followed by engulfment. Per- 

 haps the singular character of the crater of Kilauea, in Owyhee, may 

 be thought to claim for it an origin in subsidence rather than erup- 

 tion. It is described as a vast sudden depression in what would 

 otherwise be almost a level plain, on the side of the gently sloping 

 volcanic mountain of Mauna Roa. It has an irregularly oval form, 

 from three to five miles in diameter, and is usually encircled by ver- 

 tical cliffs some hundred feet high. Its bottom consists of a lake 

 of lava, on some points (which occasionally change their situation) 

 in continual ebullition, and at a white heat ; but coated over for the 

 most part by an indurated crust upon which it is often possible to 

 walk. Sometimes, however, the incrusted portion is in the centre 

 of the lake, forming a rough platform, surrounded by a circle of 

 incandescent and seemingly fused lava, — sometimes the outer circle 

 forms a solid shelf, within which an inner basin of lava boils at a 

 greater or less depth below its edge. It is evident, from the inter- 

 esting story of this crater given by Professor Dana, in the * American 

 Journal of Science,' as gathered from the relations of various observers 

 during nearly a century past, that the surface of a vast boiling lake 

 of subterranean lava existing here, rises and sinks at irregular inter- 

 vals of several years in duration ; sometimes filling the entire cavity, 

 and even pouring over its outer margin sheets of a very liquid lava, 

 — sometimes sinking to a depth of a thousand feet or more, — espe- 

 cially when some outburst from a lower vent, or chain of vents, has 

 tapped the internal reservoir. But, however interesting the charac- 

 teristic features of this crater, both from the facilities it affords for 

 observation, and the great scale on which they are developed, they do 

 not seem to me to prove the origin of the cavity other than that of 

 ordinary craters. The phsenomena of Kilauea are not so exceptional 

 as, at first view, might be supposed. Visitors who looked down 

 into the great Vesuvian crater for a few years after its formation in 

 1822, saw pools of liquid and incandescent lava at its bottom, and 

 small cones of scoriae thrown up by an almost constant ebullition. 

 The difference in the violence of the explosions, and in the amount of 

 ejected scoriae, arises, no doubt, as Professor Dana very justly ob- 

 serves, from the difference in the relative liquidity of the lavas, — those 

 of Kilauea being very liquid, those of Vesuvius much more viscid 

 and unyielding*. So also during the Vesuvian eruption of 1753, 

 * Dana, ' American Journal,' 1850, vol. ix. p. 383. 



