468 Adams & Colcer — Investigation into the Flow of Rocks. 



A further study was then made of the " flow of marble " 

 under widely varied conditions of pressure, temperature and 

 time; after which the investigation was extended to a number 

 of fine-grained and more or less impure limestones ; to crystal- 

 line dolomites ; and then to a series of typical plu tonic intru- 

 sives — diabase, essexite and granite. 



A series of comparative experiments were then made for the 

 purpose of accurately measuring the loads required for the 

 deformation of standard columns of these and other rocks 

 under precisely identical conditions of differential pressure and 

 extremely slow movement. 



t In the present paper it is proposed to outline the methods 

 employed in these investigations and to present the results 

 obtained by the further study of the " Flow of Marble " ; and 

 in subsequent papers to set forth the results obtained in the 

 case of some of the other and more resistant rocks. The 

 results of the investigation as a whole when completed will 

 appear, in extended form and fully illustrated, as a Publication 

 of the Carnegie Institution of Washington. 



Methods Employed. 



In seeking to ascertain experimentally the action of differ- 

 ential pressure on rocks with a view to reproducing more or 

 less accurately the conditions of pressure which obtain in the 

 deeper parts of the earth's crust, it is manifestly quite useless 

 to attempt to reproduce these conditions by simply submitting 

 the rocks to compression in a testing machine, as is done in 

 testing the strength of materials. There is certainly differen- 

 tial pressure in this case, but it is merely the ordinary atmos- 

 pheric pressure on the sides of the test-piece, while the 

 tremendous pressure of the testing machine acts in the vertical 

 direction. It is necessary to increase the lateral pressure and 

 make it in some degree at least approach the measure of that 

 exerted in a vertical direction if the pressure conditions of the 

 deeper parts of the earth's crust are to be reproduced. The 

 material must be held in and supported laterally, so that it will 

 not readily break or fracture as the vertical pressure is brought 

 to bear upon it until at least the required conditions of differ- 

 ential pressure have been secured. 



In the deformation of rocks within the earth's crust the 

 pressure element which corresponds to this lateral resistance is 

 furnished by the great weight of overlying strata forming the 

 upper portion of the earth's crust, while the direct pressure 

 exerted by the testing machine represents the tangential thrust 

 which folds them. 



To secure this lateral resistance, two methods have been 

 proposed. The first is that suggested many years ago by 



