Orici'tn of Moil nidi II Rmujcx. — licddc 281 
inouutain-ranges, bend the crust helow the inaxinium depth of 
an}' oceanic depression. 
This necessaiT subsidence again insures the estaldisliment of 
the basin of deposition and its continuous existence. 
Disphiiinieut of iiidtfer in the Sliell of Greatest Mohilitij. 
If the matter in a shell of the earth between the nucleus and 
xi-rust is in the condition I have postulated, it is evident that a 
lateral displacement of the matter of the shell must take place to 
some extent through weighting l»v sediment, and this will have its 
ert'ect in raising the levels of the earth's crust surrounding the 
basin of deposition; l)ut will not be an agent in mountain- 
building. 
Morcincnf of the Isogeotluriiis. 
It is evident, from the variations in the rate of increase of 
temperature that exist in various localities as the crust is pene- 
trated, that the lines of equal temperature (isogeothei*ms) in the 
earth's crust are subject to change, for it is not to be supposed 
that the temperature gradients have remained in their existing re- 
lations for all time. 
It is also evident, as first shown by 13al)bage and Herschel, that 
the covering of any particular area of the earth with sediment 
Avill necessarily raise the temperature of the crust l)elow*. If. 
therefore, we assume a thickness of 1 miles of sediment to be 
laid down in a basin of deposition or earth-trough, and the rate 
<^f increase of temperature to lie one in fiftv, what were originally 
surface-rocks possessing a surface-temperature determined by the 
climate of the locality will l)e raised in temperature over 1,000° 
Fahr. , and eventually the whole of the underlying rocks of the 
earth's crust even below the shell of greatest change will be pro- 
portionately atl'ected. The 10 miles of overlying sediments under 
such conditions wouldbe raised 1,000° Fahr.. at the base, dimin- 
ishing to zero at the surface. 
Effiits if thr rise of temperature on flu Fniniilutiini Roe/.s. Jni- 
tiiil Stiiii, . 
The section of the crust of the earth weighted and heated at 
the same time will be subjected to a gradually increasing com- 
l)ressive stress. So long as the actual expansive force of the 
heated crust is insufHcient to raise the weight of sediment l)eing 
*This is well e.vplained both by Babbage and Herschel in the Uth 
Bridsrewater Treatise. 
