Mr J. D. Dana on the Volcanoes of the Moon, 19 



rounds tlie lower pit, and the various forms of the cones. , A 

 large number of the lunar craters have an inner circle 

 either as a terrace or ridge. The ledge within Timocharis 

 (fig. 1), is very similar to that of Kilauea, and is continued 

 around the whole pit unbroken as in the Hawaiian crater. 

 The other figures illustrate the same feature in different con- 

 ditions. Some of them, too, contain circular areas with the 

 rim scarcely elevated (fig. 2), and others raised into cones 

 (fig. 3) : and so, in Kilauea, there are at times boiling lakes 

 in the bottom plain, and other poojs constitute the summits 

 of cones which they themselves have formed. To appreciate 

 the comparison, it must be remembered that the Hawaiian 

 pit-crater is upwards of three miles in length, and averages 

 nearly half this in breadth ; and that the largest boiling pool, 

 though more than 1000 feet in diameter, is still a small spot 

 in the extensive area. During times of gi^eater activity, the 

 whole pit is in every part lighted with the fiery lavas, over- 

 flowing at times from the numerous lakes, and jetted from 

 the many cones. 



The circular or slightly elliptical form of the moon's cra- 

 ters is also exemplified to perfection. For the lakes of Ki- 

 lauea have this shape ; and although the pit itself is oblong, 

 owing to its situation on a fissure, other large though extinct 

 pit-craters of Mount Loa are quite as regularly circular in 

 form. Some are twins ; that is, are made up of two or threq 

 coalescing circles. 



AVe have chosen Kilauea for these illustrations, because it 

 i.s now in action, and the features appealed to have been 

 familiar to us, since the first publications of Admiral Byron, 

 and liev. Charles S. Stewart. I may add, that the facts are 

 finely illustrated in the Narrative of the Exploring Expedi- 

 tion by Captain Wilkes,* and they will be farther detailed in 

 the Expedition Geological Report on the Hawaiian Islands, 

 now in course of preparation. The exact application of these 

 facts, as far as regards general features, to the summit cra- 

 ter of Mount Loa, will be found fully sustained by the plans 

 and views accompanying the Narrative. 



* See Narrative, vol. iv., p. 125, and the map of part of Hawaii, in vol. vi. 



