day: geophysical research 251 



is a simple type. Still more recently (quite lately in fact), it 

 has occurred to many students of the earth that here lies not only 

 the clue but perhaps the key to their great problem. If the indi- 

 vidual components which are intimately mixed in solution separate 

 wholly or partially in some regular way upon freezing — and 

 nearly all the solutions which have been studied appear to show 

 such segregation — we have a quantitative system which will 

 probably prove adequate to solve the problem of rock formation, 

 provided only that the experimental difficulties attending the 

 study of molten rock and the complications imposed by the pres- 

 ence of so many component minerals, do not prove prohibitive. 

 This is a very simple statement of the point of view which has 

 led to the experimental study of rock formation in the laboratory 

 as a natural sequence to statistical study in the field. 



Geophysics therefore does not come as a new science, nor as a 

 restricted subdivision of geology, like physiography or stratig- 

 raphy, but rather to introduce into the study of the earth an 

 element of exactness, of quantitative relation. It may include 

 physics or chemistry, biology or crystallography or physical 

 chemistry, or all of these at need. The distinctive feature of 

 geophysics is not its scope, which may well be left to the future, 

 but its quantitative character. The Geophysical Laboratory of 

 the Carnegie Institution at Washington has entered upon sonic 

 of the investigations suggested by this long preliminary study of 

 the earth, — the physical properties and conditions of formation 

 of the rocks and minerals. The Department of Terrestrial Mag- 

 netism of the same institution has undertaken another, — the 

 earth's magnetism; the German Geophysical Laboratory at 

 Gottingen a third, — the earthquakes — and these will no doubt 

 be followed by others. 



The first effect of calling exact science into consultation upon 

 geologic problems is to introduce a somewhat different viewpoint. 

 It has been our habit to study the minerals and the rocks as we 

 find them today, after many of the causes which have had a 

 share in their evolution have ceased to be active, — after the fibre 

 has gone out. If we attempt to reconstruct in our minds the 

 operations which enter into the formation of an igneous rock or 



