348 F. A. Perret — Circulatory System in the 



the manner of a simple pit-crater. On the other hand, the 

 lava in its passage over the conduit has become re-heated and 

 re-vivified and will not only resist congelation to the walls but 

 may often be capable of re-melting them and thus to actually 

 excavate an extension in the direction of its flow. We may 

 confidently say that a continuance of normal conditions will 

 inevitably produce an oblong lake with circulation in the direc- 



Fig. 6. 



■_H 



■ 



Fig. 6. Telephoto view of a typical spatter-grotto. 



tion of its length and, in view of the fact that, under waning 

 conditions of activity, consolidation will occur at the sides 

 while it will be impeded at the ends, we may go further and 

 state that, as conditions approach the sub-normal — especially 

 after a normal phase — the lake will be longer and narrower, 

 while an approach to super-normal activity will result in a 

 more nearly circular form. See fig. 5. 



A final question, of great importance but difficult of solu- 

 tion, is whether or not the conduit proper is interested in the 

 scheme of the lake's circulation, — whether, that is to say, a 

 portion of the downflowing lake lava descends into the conduit 

 with a corresponding rise at the other side from the conduit to 

 the lake, as indicated in the diagram by the arrows marked 

 with interrogation points ? Daly, in a beautifully written 



