GEOPHYSICAL RESEARCH — ADAMS. 231 



In the case of these harder rocks the aim of the investigation 

 was to determine not only the nature and extent of the movements 

 induced by pressure, but also to measure the strength of the rock 

 before and after deformation. Curiously enough, while this measure 

 of relative strength can be made in the case of marble, it has been 

 found impossible, so far, to determine it in the case of the rocks in 

 question, owing to the fact that upon the removal of the steel which 

 surrounds the rock during the deformation the relief of pressure 

 develops cracks which run through the rock in certain directions. 



The nature and mechanism of the flow developed in the rocks have, 

 however, been determined. A series of experiments have also been 

 carried out to ascertain whether after the deformation of the marble 

 in the cold the rock will recover its strength on resting or by heating, 

 as in the case of steel. 



An investigation into the nature of the deformation suffered by 

 crystals of various rock-making minerals when submitted to pressure, 

 after having been embedded in fused alum, fusible metal, sulphur, 

 and other solids, and then inclosed in strong tubes of copper, has 

 been carried out and is nearly completed. 



A series of experiments has also been carried on with a view to 

 measuring the force required to deform standard columns of different 

 rocks under identical conditions of plastic flow, and thus to measure 

 the relative plasticity of these several rocks when they are caused to 

 move by stress in the earth's crust. 



During the past summer apparatus has been constructed and 

 material prepared for the completion of these several investigations, 

 and for the extension of the work during the coming year to the 

 harder crystalline rocks, such as granite and diabase. 



Biblioeraphy of Geophysics. — For report on this subject, see under 

 Bibliography, page 86. 



