INORGANIC GEOLOGICAL DYNAMICS. 615 



such attempts would belong, is hardly yet ripe for 

 such speculations. But when we look at the uni- 

 versal prevalence of crystalline forms and cleavages, 

 at the extent of the phenomena of slaty cleavage, 

 and at the segregation of special minerals into veins 

 and nodules, which has taken place in some un- 

 known manner, we cannot doubt that the forces of 

 which we now speak have acted very widely and 

 energetically. Any elucidation of their nature would 

 be an important step in geological dynamics (HA). 



Sect. 6. Theories of Changes of Climate. 



As we have already stated, Geology offers to us 

 strong evidence that the climate of the ancient 

 periods of the earth's history was hotter than that 

 which now exists in the same countries. This, and 

 other circumstances, have led geologists to the in- 

 vestigation of the effects of any hypothetical causes 

 of such changes of condition in respect of heat. 



The love of the contemplation of geometrical 

 symmetry, as well as other reasons, suggested the 

 hypothesis that the earth's axis had originally no 

 obliquity, but was perpendicular to the equator. 

 Such a construction of the world had been thought 

 of before the time of Milton 10 , as what might be 

 supposed to have existed when man was expelled 



10 Some say he bade his angels turn askance 

 The poles of earth twice ten degrees and more 

 From the sun's axle, &c.- Paradise Lost, x. 214. 



