354 J. LeConte—Formation of the 
, 2. Mountain Chains. 
A cooling earth may be regarded as composed of concentric 
isothermal shells, each cooling by conduction, and in the case 
of liquid also by convection to the next outer and the outer- 
most by radiation into space. Furthermore under these condi- 
le ss. é 
No other view but this will, I think, satisfactorily explain 
age. 
It is now established beyond the possibility of a doubt, by 
the beautiful observations and experiments of harpe, Soe 
by pow 
ful pressure perpendicular to the planes of cleavage, by which 
the whole rock-mass has been mashed together and shortened m 
that direction, and correspondingly extended in the direction of 
the planes of cleavage. As the planes of cleavage are usually 
ination. This plication is always associated with cleavage, a 
vice versa, cleavage, when the rock material is suitable for devel 
