690 CROSS, IDDINGS, PIRSSON, WASHINGTON 



The petrographer who believes that these fundamental points 

 are correct and who is willing to accept them will not wish to 

 reject the whole system because he may not agree with some of 

 its minor features, but the one who does not accept the funda- 

 mental points will have no use for this system, or an}' of its 

 features, great or small. 



At first it will not be easy for the petrographer to think of 

 rocks as expressed in this system ; it will require some use and 

 experience. Nearly everywhere over the whole field it intro- 

 duces new conceptions, and we firmly believe more correct and 

 logical ones than have hitherto prevailed. We have made no 

 attempt to modify, or patch up, or define the older previous 

 systems, for we believe that the day for efforts of that kind has 

 passed ; that they have had their use and should now be replaced 

 by something more in accord with the results of the great 

 amount of recent investigations, and of our present knowledge, 

 and therefore better adapted to present and future needs. It is 

 of course easier to patch and wear old garments than to make 

 new ones, but to confess this fact as controlling one's attitude 

 toward new propositions would be merely to acknowledge a 

 condition of mental supineness. 



If petrographers believe this system to be an advance over 

 previous ones, we offer no apology for imposing a new mental 

 burden upon them, for it is obvious that the ever-increasing 

 accumulation of knowledge of the chemical and mineral proper- 

 ties of rocks, and of their relations to one another and to their 

 texture, mode of occurrence, and their origin impose a greater 

 task on modern petrographers than was borne by those of a 

 former generation. And since it is not to be assumed that the 

 present state of petrographical knowledge is complete, provision 

 should be made for expansion and adjustment along lines which 

 seem to be those in which future development will take place. 



Whitman Cross, 

 Joseph P. Iddings, 

 Louis V. Pirsson, 

 Henry S. Washington. 



