Vol. 4] Thelen — Thermal Conductivities of Certain Schists. 203 



The answer seems to be very definitely, No ! that the thermal 

 conductivity of a rock is not in any way a function of the 

 orientation in itself of its mineralogical constituents, but is en- 

 tirely the result of the integrated thermal conductivities of the 

 individual minerals.* 



This result was the probable one. Experimental verification 

 is, however, always valuable and grateful. 



When sufficient evidence shall have accumulated to verify 

 the above answer and the analogous statement concerning dilata- 

 tion effects, namely, that, the dilatation coefficients of a schist 

 are unequal in different azimuths and computable from a micro- 

 scopic examination of the rock structure and a knowledge of 

 the dilatation coefficients of the constituent minerals, we shall 

 have a new and potent tool to take into account in any discussion 

 of deformations of the earth's crust by thermal effects. Sup- 

 pose, for example, a bed of crystalline schists undermined by a 

 molten magma. If the coefficient of thermal expansion in one 

 direction in the overlying plane is greater than in another direc- 

 tion perpendicular to the first, and in the same plane, then we 

 shall have a definite tendency toward differential deformation. 

 The effects will duplicate those clue to compression by other 

 agencies. Take, for instance, a quartzose rock. This is a poor 

 example since quartz, though often found in schists with the 

 longer dimensions of the individual grains roughly parallel, is 

 yet never found with its c axes parallel. But the physical con- 

 stants of quartz have been worked out and can furnish the basis 

 of a numerical computation. For the range from 0° to 100° C, 

 Fizeau gives that parallel to c, 



h = lo ( 1 + . 0001 )072 1+ . 01 X )000008 If) 

 and perpendicular to c, h = k (1+ .000013 <+ .000000012 H. 



If we make £ = 100°C, we have hoo— k (1.00078) parallel to 

 c and /ioo = h (1.00141) perpendicular to c. 



Waldemar Voigt determined Young's modulus in various 



*Such effects as total reflection, for instance, are probably not entirely 

 negligible. A Sillimanite needle, surrounded entirely by minerals of lower 

 index of refraction than its own, would propagate in the direction of its 

 length only any heat ray that entered a cross section of the needle nearly 

 parallel to its length. The effect may be observed by looking lengthwise 

 through a solid glass tube which points toward a source of light— light and 

 heat waves obeying the same laws in general. 



