264 A CENTURY OF SCIENCE 



the future. The accumulation of the exact physical and 

 chemical data, which is its aim, will serve as a necessary 

 check to hypothetical speculation and bring petrology, 

 and especially petrogenesis, in line with the other more 

 exact sciences by furnishing quantitative foundations for 

 its structure of theory to rest upon. 



While the achievements of this great organization seem 

 to minimize the work of the individual investigator in 

 this field, he may take heart by observing the important 

 results on the strength of rocks under various condi- 

 tions which have been obtained by Adams in recent years, 

 data of wide application in theoretical geology. In this 

 field also a special text has appeared in which the prin- 

 ciples and acquired data are given. 45 



Summary. 



In this brief retrospect, giving only the barest outlines 

 and omitting from necessity much of importance, we have 

 seen petrology grow from occasional crude experiments 

 into a fully organized science in the last half century. It 

 has to-day a well-perfected technique, a large volume 

 of literature, texts treating of general principles, of 

 methods of work, descriptive handbooks on the morph- 

 ological side, and has attained general recognition as a 

 field, which, though not large, is worthy of the concen- 

 tration of intellectual endeavor. Like other healthy 

 growing organisms it has given rise to offshoots, and the 

 sciences of metallography and of the micro-study of 

 ore deposits, which are rapidly assuming form, have 

 branched from it. 



What of the future ? The old days of mostly descrip- 

 tive work, and of theorizing purely from observed results, 

 have passed. The science has entered upon the stage 

 where work and theory must be continually brought into 

 agreement with chemical, physical and mathematical 

 laws and data, and in the application of these new prob- 

 lems present themselves. As we climb, in fact, new hor- 

 izons open to our view indicating fresh regions for 

 exploration, for acquiring human knowledge and for 

 our satisfaction. 



