492 Mr. T. M. Reade on the Origin of Mountain- Ranges 



form a complex which will be simultaneously, but differentially, 

 affected by the folding and elevation when that begins. 



Unlocking the Igneous Forces of the Earth. 



When once the elevation initiated only by piling-up of 

 sediment, the sinking of the crust, and its consequent heating 

 — otherwise by the rise of the isogeotherms — is established, 

 a movement of the interior heated matter of the earth must 

 take place towards the axis or axes of the range. This is 

 proved by the frequency of granitic cores in great mountain- 

 ranges, by the volcanic action accompanying their elevation, 

 and its persistence or recurrence in a range even late on in 

 its history, as instanced by the Andes, Rockies, and the 

 mountains of the Caucasus, where volcanic cones surmount 

 some of the highest granitic peaks, showing that these are the 

 lines of least resistance through which the interior forces of 

 the Earth expend themselves. 



Heating of the Rocks of a Mountain-Range recurrent and 

 constantly renewed during its History. 



It is thus seen that the heated interior matter of the Earth 

 is constantly being drawn towards and injected into the 

 constituent framework of a mountain-range. When once the 

 elevation of the sediments consolidated into rocky matter in 

 the earth-trough begins through the influence of lateral 

 pressure and the expanding mass beneath, a reduction of 

 pressure and increase of volume takes place in the underlying 

 fused rock. The compressive stresses of the rigid rock are 

 partially relieved by folding and upward flow, and the tempe- 

 rature of the mass falls. Additional fused matter has been 

 drawn from the interior, and in process of time the rocks of 

 the range begin again to rise in temperature. Such fluctu- 

 ations of temperature are well shown in the intermittent 

 character of volcanic action. After a great outflow of lava, 

 a volcano is quiescent sometimes for centuries. It has lost so 

 much matter and so much heat, but the forces accumulate 

 during the time of quiescence to burst forth with renewed 

 vigour. Such intermittent activity I conceive is what takes 

 place on a larger scale in the history of a mountain-range, 

 but with greater time-intervals. 



Dynamical Effect on the Strata of the Crust hy Rise of 

 Temperature. 



The effect of a rise of temperature on the rocks of the Earth 

 is, excepting in the case of unconsolidated clays, to increase 



