GENERAL PLAN RELATION TO GEOLOGICAL RESEARCH. I J 



between the states of matter, which have been established for mode- 

 rate temperatures, must be regarded as more or less tentative and 

 subject to eventual revision. We have been accustomed to assume, 

 both in geology and in physics, with rather more confidence than 

 scientific experience justifies, that established relations for ordinary 

 temperatures and pressures will hold in comparable ratio for the higher 

 temperatures and pressures also. Experimentation under extreme 

 conditions is slow and technically difficult, and it is, therefore, not 

 strange that simple relations which are verifiable within easily acces- 

 sible conditions should now and then be accorded the dignity of 

 natural laws without sufficient inquiry into the more remote con- 

 ditions. 



GENERAL PLAN. 



Our plan on entering this field was to study tne thermal behavior 

 of some of the simple rock-making minerals by a trustworthy method, 

 then the conditions of equilibrium for simple combinations of these, 

 and thus to reach a sound basis for the study of rock formation or 

 differentiation from the magma. Eventually, when we are able to 

 vary the pressure with the temperature over considerable ranges, our 

 knowledge of the rock-forming minerals should become sufficient to 

 enable us to classify many of the earth-making processes in their 

 proper place with the quantitative physico-chemical reactions of the 

 laboratory. 



RELATION TO GEOLOGICAL RESEARCH. 



The relation which this plan bears to general geological research 

 may perhaps be expressed in this way. Geological field research is 

 essentiallv a study of natural end-phenomena, of completed reactions, 

 with but a very imperfect record of the earlier intermediate steps in 

 the earth-making processes. The records of the splendid laboratory 

 experiments in rock synthesis which have already been made are also 

 of this character. The final product has been carefully studied, but 

 the temperatures at which particular minerals have separated out of 

 the artificial magma, and the conditions of equilibrium before and 

 after such separation, have not been determined. In fact, except for 

 a limited number of determinations of the melting points of natural 

 minerals, no exact thermal measurements upon minerals or cooling 

 magmas have been made, and it is in this direction that a beginning 

 is to be attempted. The temperatures of mineral reactions under 

 atmospheric pressures are nearly all within reach of existing labora- 

 tory apparatus and methods. 



