648 THE POPULAR SCIENCE MONTHLY. 



ronment are familiar to every geologist who has availed himself 

 of the newest and most potent aid in his profession. There is 

 nothing hypothetical about them, for the minerals have written 

 their own " life-histories " in characters which can not be misread. 

 They throw a flood of light upon many types of rocks whose ori- 

 gin and nature have heretofore remained an unsolved riddle ; and 

 they open up a vista of possibilities to the future explorer whose 

 length and whose attractiveness can hardly be exaggerated. 



Let me quote, in closing this brief survey of a new field in 

 geology, a single passage from Prof. Judd : 



" In the profound laboratories of our earth's crust," he says, 

 " slow physical and chemical operations, resulting from the inter- 

 action between the crystal, with its wonderful molecular struct- 

 ure, and the external agencies which environ it, have given rise to 

 new structures, too minute, it may be, to be traced by our micro- 

 scopes, but capable of so playing with the light- waves as to startle 

 us with new beauties, and to add another to 



' The fairy tales of science, 

 And the long results of time.' 



" Yes ! minerals have a life-history, one which is in part deter- 

 mined by their original constitution, and in part by the long 

 series of slowly varying conditions to which they have since 

 been subjected. ... In spite of the limitations placed upon us by 

 our brief existence on the globe, it is ours to follow, in all its 

 complicated sequence this procession of events; to discover the 

 delicate organization in which they originate ; to determine the 

 varied conditions by which they have been controlled; and to 

 assign to each of them the part which it has played in the won- 

 derful history of our globe during the countless ages of the past. 



" Mineralogy has been justly styled the alphabet of petrology ; 

 but if the orthography and etymology of the language of rocks 

 lie in the province of the mineralogist, its syntax and prosody 

 belong to the realm of the geologist. In that language, of which 

 the letters are minerals and the words are rock-types, I am per- 

 suaded that there is written for us the whole story of terrestrial 

 evolution." 



Concluding its review of the report of the Krakatoa Committee of the Royal 

 Society, "Nature" calls attention to the fact that the study of the sequela} of 

 the great explosion "has not merely enlarged our conceptions of volcanic powers 

 and the continuity of atmospheric circulation, as well as yielded positive informa- 

 tion of great value to different branches of science, but has opened up fresh prob- 

 lems in optical and meteorological physics, the attack and solution of which will 

 stimulate research as well as materially advance the boundaries of our present 

 knowledge of these subjects." 



