234 Messrs. II. S. Il.-Ii-Sliaw and A. Hay. 



in the C'.'irrara marMe. In six other cases the structures bore n 

 analogies to those in the deformed rock but were of doubtful origin, 

 while in the remaining twenty the structure was different. 

 The following is a summary of the results arrived at : 

 1. By submitting limestone or marble to differential pressures ex- 

 ivcding the elastic limit of the rock and under the conditions described 

 in this paper, permanent deformation can be produced. 



i'. This deformation, when carried out at ordinary temperatures, is 

 due iii part to a cataclastic structure and in part to twinning and 

 gliding movements in the individual crystals comprising the rock. 



3. Both of these structures are seen in contorted limestones and 

 marbles in nature. 



4. When the deformation is carried out at 300 C., or better at 

 400 C., the cataclastic structure is not developed, and the whole move- 

 ment is due to changes in the shape of the component calcite crystals 

 by twinning and gliding. 



5. This latter movement is identical with that produced in metals 

 by squeezing or hammering, a movement which in metals, as a general 

 rule, as in marble, is facilitated by increase of temperature. 



6. There is therefore a flow of marble just as there is a flow of 

 metals, under suitable conditions of pressure. 



7. The movement is also identical with that seen in glacial ice, 

 although in the latter case the movement may not be entirely of this 

 character. 



8. In these experiments the presence of water was not observed to 

 exert any influence. 



9. It is believed, from the results of other experiments now being 

 carried out but not yet completed, that similar movements can, to a 

 certain extent at least, be induced in granite and other harder crystal- 

 line rocks. 



" Lines of Induction in a Magnetic Field." By H. S. HELE-SHAW, 

 F.If.S., and A. HAY, B.Sc. Received June 13, Read -Turn- 

 21, 1900. 



(Abstract.) 



When a viscous liquid flows in a thin layer between close parallel 

 walls, the motion takes place along stream-lines identical with those of 

 a perfect liquid. The course of the stream-lines may be rendered 

 evident by injecting into the clear liquid thin bands of coloured liquid. 



If the thickness of the liquid layer be varied, then there will lie .1 

 decrease of resistance to the flow wherever there is an increase of 



