February, 1907.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



29 



solid crust resting on the liquid mass was thinner, so that 

 the channel communicating with the three reservoirs of 



Fig. 5. — Lava Lake in Kilauea 



molten lava was shorter and wider, thus offering a freer 

 passage to the liquid flow. 



Professor 

 Pickering di- 

 vides terrestrial 

 craters into 

 three classes, 

 according to the 

 materials of 

 which they are 

 composed. 



(i.) Tufa cones 

 of hardened vol- 

 canic mud. 



(ii.) Cinder 



cones. 



(iii.) Lava 



craters. 



It is this third 

 class where 

 steam or water 

 is less involved 

 in the process 

 of eruption 

 which most 

 resembles what 

 we find on the 

 Moon. 



This class may 

 be again divided 

 into four sub- 

 classes accord- 

 ing to the shape 

 of the craters— 

 (f) lava rings, and (d) lava bowls. Taking the first of 



them (a), the lava cones, these often emit vast volumes 

 of lava which may extend for miles in broad streams. 



The second 

 sub-class (6), the 

 lava pits, are by 

 far the most 

 numerousgroup 

 and are widely 

 distributed 

 through the 

 Hawaiian Is- 

 lands. They 

 have no outer 

 slopes what- 

 ever, consisting 

 simply of a pit 

 sunk in the 

 ground. Their 

 inner walls are 

 sometimes ver- 

 tical, sometimes 

 inclined, and 

 descending with 

 a steep slope to 

 a flat floor. 



The lava 

 rings (f ) are the 

 rarest type in 

 Hawaii, and 

 resemble the 

 larger craters 

 found on the 

 Moon. 



The lava 

 bowls (d) differ from'them in that^the bottom, instead of 

 presenting a well-defined, flattened floor, is concave, the 



Pig. 6. Lava Lake in kilauea. 



namely, (a) lava cones, (b) lava pits. 



curvature being continuous with the walls. They are iden- 

 tical in appearance with most of the smaller lunar craters. 



