54 



KNOWLEDGE & SCIENTIFIC NEWS. 



| March, 1907. 



was 25 feet. A stream of lava had poured from the 

 summit, l>ui had not i^ni far beyond the rim. There 

 may have hem as mam as 50 rudimentary craterlets 

 scattered over the floor, in all stages ul growth, Irom a 



lava would have completely destroyed them, forming a 

 series of crater pits, into which the lava would have 

 subsequently retreated. In the south-eastern portion 

 two such piis were found, perhaps 30 feet in diameter, 





Fig. 3.— Pinnacles Maie Imbrium. 



hardly-noticeable elevation to the complete craterlet 

 shown in the figure. . . . "If the volcanic forces 

 beneath these craterlets," observes Professor Pickering, 

 " had been more intense, it is probable that the issuing' 



Fig. 5.— Crack, KHauea. 



Fig. 4.— Ariadaeus Rills. 



down which the lava had poured, but had solidified 



without filling them up. 



After the craters, among the most important features 



of the lava floors, are the elevated formations — the 



spiracles, 

 pi n nac les, 

 and ridges. 

 When the 

 gases work 

 their way up 

 to the sur- 

 face they 

 escape by 

 little blow- 

 holes. In so 

 doing they 

 often carry 

 small quanti- 

 ties of lava 

 along with 

 them. This 

 lava quickly 

 hardens on 

 reaching the 

 surface, and 

 builds up 

 around the 

 aperture a 

 tube, which 

 P ro f e sso r 

 P i cl<e ring 

 calls a spir- 

 acle. Some- 

 times it is 

 closed at the 



