90 REPORTS ON INVESTIGATIONS AND PROJECTS. 



employed by physical chemists in systems of four and five components will 

 require to be completely remodeled for the study of complicated silicates. 



From this outline it will be seen that the establishment of a geophysical 

 laboratory for the serious quantitative study of rock formation encounters 

 its chief difficulties, and therefore applies its greatest effort in the opening 

 years of its development, in the solution of questions of purely physical and 

 physico-chemical origin; that is, in the perfection of its tools; and it is 

 equally interesting to know that the results of these efforts are of equal value 

 to the older sciences. 



To carry the discussion further upon these lines would be to exceed the 

 limits of an annual report of progress. It will therefore be better to turn 

 to one of the mineral problems upon which we have been engaged for a con- 

 siderable time, in which positive conclusions have now been reached which are 

 not only of considerable value to petrologists but also to one of our important 

 national economic interests. As soon as it had proved practicable to estab- 

 lish the relations of two stable minerals throughout all the conditions of 

 change to which they may have been subjected in nature, it became impor- 

 tant to know whether the complications introduced by adding a third and 

 eventually a fourth mineral would yield to the same methods of analysis. 

 The complicated character of natural rocks makes this question of the very 

 first importance from the geological viewpoint. A system of three of the 

 most important oxides entering into the composition of rocks — silica, lime, 

 and alumina — has, therefore, been under investigation for a considerable 

 time, and a preliminary report of it is now in press. The scope of such an 

 investigation and some of its difficulties will perhaps be appreciated from the 

 fact that it involves the interaction of fourteen minerals, with the formation 

 of sixteen ternary eutectics. Inasmuch as this is perhaps the first time that 

 a three-component system of silicates has ever been seriously studied from 

 this viewpoint, it is a most interesting and important investigation and hardly 

 admits of concise review. In it we have not only been able to establish the 

 equilibrium relations obtaining in a complicated group of minerals, but we 

 obtain for the first time a true conception of what might be expected to 

 happen when a magma of certain composition is intruded into limestone or 

 sandstone in such quantity that considerable portions of the older rock have 

 redissolved and affected the composition of the magma. It also offers for 

 the first time in laboratory experience a case of resorption of a mineral which 

 formed early in the cooling process, dissolved, and afterward reappeared in 

 other relations in which neither a change of pressure nor any sudden change 

 of conditions interfered to interrupt the cooling process. 



This experimental demonstration of resorption becomes of great interest 

 to petrologists in that it bears directly on the classical question of the order 

 of crystallisation from the magma. In the present instance the first crystals 

 to separate redissolve and disappear in the magma. The true order of crys- 

 tallization is, therefore, not that which the study of the cold rock would lead 

 one to believe. Furthermore, this relatively simple ternary system affords 



