6io CHARLES R. VAN HISE 



deformation made it possible to formulate the principles controlling 

 the interior transformations of rocks. In a similar manner these 

 problems interlock with the other problems of physical geology, and 

 physical geology interlocks with the other sides of the subject. The 

 whole science is one interlocking system, a part of which cannot be 

 satisfactorily developed independently of the other parts. For 

 instance, weathering can be placed in order only when considered in 

 connection with general metamorphism, erosion, and sedimentation. 

 Ore deposits can be explained only by combining the principles of 

 volcanism, deformation, metamorphism, etc. 



In attempting to reduce a small part of the subject of geology 

 to order under the principles of physics and chemistry, the plan was 

 followed of oscillating between observations of the facts as exhibited 

 in the field and laboratory, and their physical-chemical explanation. 

 After a large number of facts were observed in the light of known 

 principles, the attempt was made better to formulate the principles 

 which explain them. After this was done, the facts were again more 

 comprehensively studied in the field and in the laboratory in the light 

 of the new principles. The statement of principles was then modified 

 and improved by use of the new facts. The improved statement of 

 principles was again tested by further facts. Thus the process of 

 development has been a series of approximations toward both com- 

 pleteness of statement of fact and perfection of formulation of principle, 

 but neither have been attained, nor, so far as we can see, will they ever 

 be reached. 



NECESSITY FOR ADVANCE IN THE SCIENCES OF PHYSICS AND 

 CHEMISTRY. 



Very often, in the attempt to find principles applicable to the 

 phenomena of deformation and metamorphism, it has been found 

 that the science of physics-chemistry is not sufficiently advanced to 

 make this possible. In such cases physicists and chemists have been 

 asked to develop this subject at the needed points. But at innumer- 

 ble places the problems have proved to be so numerous and complex 

 that the necessary aid has not been obtainable. Thus there has 

 arisen, with reference to my own work, a great line of unsolved 

 problems which demand the co-operation of physicists and chemists. 

 The same is true of the work of all other geologists interested in the 



