520 GEOPHYSICS 



the mathematical conditions for steady flow can be worked out, and 

 if these are not consistent with the facts of the globe, a vera causa 

 for upheaval will have been found, which may lead to further and 

 more detailed conclusions. It should also either elucidate or simplify 

 the subject of the fusion of magmas and their eruptive expulsion. 



The data for constitution and thermal diffusivity will readily 

 be applicable to the problem of the earth's age and will yield a cor- 

 rected value of the probable lapse of time since the initiation of the 

 consistentior status of the Protogaea. 



The most difficult field in geophysics is the study of solutions at 

 high temperatures. This is largely because both methods and appara- 

 tus require to be invented. When work of this kind was undertaken 

 in the laboratory of the Geological Survey, three years since, no 

 furnace existed in which pure anorthite could be melted and a trust- 

 worthy determination of the temperature of fusion made. For the 

 study of aqueo-igneous fusion, which must, of course, be performed 

 at considerable pressures, extremely elaborate preparation is neces- 

 sary; indeed, all attempts hitherto made in this direction have been 

 only very partially successful. 



Were it not that the number of important rock-forming minerals 

 is small, the study of igneous solutions for geophysical purposes 

 would be an almost hopeless task. The feldspars, the pyroxenes, the 

 amphiboles, and the micas appear to form isomorphous series, and 

 must be studied as such. They, with quartz, make up nearly 93 per 

 cent of the igneous rocks, nepheline, olivine, leucite, apatite, magne- 

 tite, and titanium minerals substantially completing the list which 

 enter into these rocks in sensible proportions. After the melting- 

 points of the minerals have been determined and their isomorphism 

 has been studied, the most important research to be undertaken is 

 that on their eutectic mixtures. Other features, however, must receive 

 attention, such as their latent heat, ionization, viscosity, and diffusiv- 

 ity. Immensely interesting will be the study of melts into which 

 hydroxyl enters as a component and which may turn out to be 

 emulsions rather than solutions. Such researches will constitute a 

 most substantial addition to physical science, and, as pointed out 

 above, offer a good prospect for the rational classification of rocks. 



Enough has been said to show how closely geophysical researches 

 interlock. Researches at high temperatures must accompany inves- 

 tigations at common temperatures, physics must be supplemented 

 by physical chemistry, mathematical ability of the highest order 

 must be called upon at every step to elucidate difficulties and to draw 

 inferences capable of being again submitted to inquiry, and some 

 geological knowledge, too, is requisite to appreciate the bearing 

 of results and to indicate the questions of importance. No human 

 being has the length of days, the strength, the skill, or the knowledge 



