180 F. D. ADAMS EXPEPvIMEXT IX GEOLOGY 



that is to say, a pressure from all sides, l^nt much greater in one direction 

 than in the others — was required. This condition was secured by inclos- 

 ing very accurately turned and polished cylinders of Carrara marble in 

 heav}^ tubes of nickel steel of ^Deculiar form and fitted with pistons of 

 chromium tungsten steel. 



It was found that by the application of differential pressure alone a 

 perfect deformation of the marble Avas obtained — the rock flowed as a 

 column of soft metal might. If the movement was allowed to go forward 

 very slowly, the rock was deformed without loss of strength. 



The action of pressure combined with heat was then examined, and it 

 was found that when the rock was heated to 300° C. or 400° C. — a heat 

 which is too low to disassociate the molecule — the movement takes place 

 more readily, and may therefore be carried out more quickly without 

 impairing the original strength of the rock. 



The third factor, that of moisture, was then introduced and the rock 

 was slowly deformed through a period of two months, while maintained 

 at a temperature of 300° C. and with steam being forced through it while 

 the deformation was going forward. The presence of moisture in this 

 experiment was found to produce no noticeable effect; the character of 

 the deformation was identical with that where pressure and heat alone 

 were employed. 



A study of thiii-sections of the deformed limestone, moreover, showed 

 quite clearly the nature of the movement which had taken place. It was 

 a movement on the gliding planes of the individual calcite crystals com- 

 posing the rock, accompanied by a fine polysynthetic twinning, each of 

 the original grains becoming in this way elongated, so that a schistose 

 structure was developed in the rock. 



This structure, furthermore, is exactly that which is displayed by cer- 

 tain of the limestones of highly contorted regions, so that we have experi- 

 mental demonstration that in these cases pressure alone would have been 

 quite adequate to produce the phenomena observed. 



Leaving this question of the deformation of marble, we may turn to 

 other rocks. 



When various impure limestones, such as those which are commonly 

 found in the Paleozoic and Mesozoic succession, were examined, it was 

 found experimentally that they could also be deformed by simple pres- 

 sure, with a development of the same schistose structure. This is also 

 true of alabaster, steatite, serpentine, and other of the softer rocks. 



With the harder rocks, such as granite, diabase, and essexite, it was 

 again found that pressure would produce a deformation of the rock with 

 the development of a schistose or foliated structure. In these cases, also, 



