124 CARNEGIE INSTITUTION OF WASHINGTON. 



rock formation, but rather during the period before the soHdification 

 of the magma than after and rather in the sense of preventing the 

 escape of gases and volatile matter which otherwise would have had 

 little or no part in the soHdification process. Thus we see that 

 pressure has had most important effects, (1) in determining the 

 composition of rocks b.y assuring the presence and chemical activity 

 of the gases and volatile ingredients which otherwise might have 

 escaped, and (2) throughout all dynamic activity in which consider- 

 able pressure differences are set up in the solid portions of the crust. 



To reach a proper conclusion about the manner of mineral and 

 rock formation upon the earth, it is therefore necessary to consider 

 pressure and temperature conjointly in appropriate magnitudes, as 

 well as to pay due attention to the character of the compression, 

 whether uniform or other\\dse. If we choose, as indeed it has been 

 our habit to do, to study the formation of minerals under high 

 temperature alone (crystallization from ''dry" melts), this is merely 

 a provisional expedient in the interest of simplicity; it enables us 

 to distinguish the different active forces and to measure them sepa- 

 rately instead of confronting the cumulative effect of a group of 

 forces which we can not in the first instance analyze. We shall be 

 much better equipped to attack the problem in its full complexity 

 after its component factors have been separately studied. 



There is no intention to intimate that studies of the joint action of 

 high temperature and pressure are entirely novel. Indeed, the 

 published work of the year — of which a summarized account may be 

 found later in this report — is in part devoted to a detailed analysis of 

 numerous papers bearing more or less directly upon this subject, and 

 there are still other publications describing a variety of apparatus 

 which is designed to find application in the prosecution of such 

 studies. Nevertheless, there has been no study of mineral formation 

 at high temperature and pressure under conditions such that the 

 various factors which enter into such formation — pressure, tempera- 

 ture, the concentration of the ingredients, both volatile and other, 

 the time of reaction, etc.— were all under control and accurately 

 measurable. Indeed, it is nearly impossible to repeat any of the 

 experiments hitherto described because of failure to control or to 

 measure one or more of these essential factors, and for the same 

 reason it is extremely difficult to draw valuable conclusions from the 

 great body of that work. It is a situation of peculiarly anomalous 

 character thus to stand at the threshold of a field of activity which 

 has been cultivated at intervals for fifty years or more without being 

 able to command any securely established vantage-point by gaining 

 which the investigator might hope to accelerate his progress. 



During the past year several attempts have been made in this 

 Laboratoiy, partly by analysis and partly by experimental measure- 



