COMMENTS. ^ 279 



total effect would be to accelerate cooling and to lower the rate of in- 

 crease observed after a certain time from what it would otherwise be, and 

 thus cause an overestimate of the time of cooling, if it were computed 

 from a given rate of increase noticed at the surface without allowing 

 for them. 



Suggested Lines of Inquiry. 



As no theor}^ is worth much which does not suggest inquiry, I would 

 in conclusion point out some of the promising lines of research opened 

 up. 



The temperature and physical conditions of acid lavas are very im- 

 l)erfectly knoAvn. 



The association of depth of earthquake shocks and character of lavas 

 in volcanoes has not been studied. 



There has been almost no study of the enclosures occurring in basic 

 plutonics. 



The contact-zones of porphyries have not been studied or their absence 

 stated with sufficient definiteness. 



The study of the oxidation of iron in reliably fresh rocks promises 

 important results. 



The further chemical examination of gases occluded in meteorites and 

 volcanic glasses would be instructive in connection with the questions 

 herein discussed. 



COMMENTS. 



The foregoing is the paper as presented to the Society at the Boston 

 meeting, but aS public discussion, by reason of the crowded program, 

 was not possible on that occasion, I desire to add a few words chiefly in 

 report of private remarks made by members who were present at the 

 reading of the paper and one of whom, at least, had expressed a desire 

 to be heard concerning it. 



Mr Darton called my attention to the interesting fact that Professor 

 William Libbey, Junior, of Princeton, N. J., who made somewhat ex- 

 tended observations among the extinct and active volcanoes of the 

 Hawaiian islands, had noticed gas lines in the spectra of glowing lavas — 

 an excellent means of determining- not only the presence of gases, but 

 their comi)osition as well. 



Professor Kemp referred to an earthquake which occurred in the 

 western United States and which is said to have had its source at a depth 

 of more than fifty miles. He also called attention to the abundance of 

 sulphur beds in volcanic regions as indicating the importance of that 

 mineralizer. 



