20 The American Geologist. January. 1905 
Were it not that the number of important rock-forming 
minerals is small, the study of igneous solutions for geophys- 
ical purposes would be an almost hopeless task. The feld- 
spars, 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, magnetite 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 re- 
search to be undertaken is that on their eutectic mixtures. 
Other features, however, must receive attention, such as 
their latent heat, ionization, viscosity and diffusivity. Im- 
mensely 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, ofifer a good prospect for the ra- 
tional classification of rocks. 
Enough has been said to show how closely geophysical 
researches interlock. Researches at high temperatures must 
accompany investigations at common temperatures, physics 
must be supplemented by physical chemistry, mathemtaical 
ability of the highest order must be called upon at every step 
to elucidate difhculties and to draw inferences capable of be- 
ing again submitted to inquiry, and some geological knowl- 
edge, 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 knowl- 
edge needed to undertake, without help, the investigation of 
geophysics as a whole. Only a few of the topics touched 
upon in the earlier pages of this essay are independent of co- 
operation ; for instance, the astronomical conditions favor- 
able to glaciation and perhaps the application of the mathe- 
matics of capilarity to the problem of erosion. On the other 
hand, the list of geophysical problems requiring co-operation 
could be almost indefinitely extended even now, and will be 
supplemented when the most pressing questions approach 
their answers. 
