Niles.] 280 [April 5, 



GENERAL CONSIDERATIONS. 



These manifestations of geological power under such different 

 geographical and geological conditions lead to a further considera- 

 tion of the distribution, importance and origin of this force. 



The disclosure of a power at five different localities, having a 

 geographical range of five and a half degrees of longitude, shows 

 that it is not a local but a widely distributed force. The exact cor- 

 respondence in the characteristics of the phenomena at each locality 

 demonstrates its identity, while the fractures and displacements of 

 rock reveal the energy of its action. A physical force so efficient and 

 extensive in its operations must be regarded as a geological agency 

 of great importance. While the study of flexed and dislocated strata 

 has led to correct conceptions of the " characteristics of the force 

 engaged," it is at least a gratification to witness its operations, espe- 

 cially as they so forcibly confirm the results which others have so 

 studiously obtained. While Prof. Dana and others have already un- 

 folded so much of the past history of this power, these phenomena 

 demonstrate its continued activity, exhibit its agency, and enlarge 

 our opportunities for interpreting the records of the past through 

 the light of present events. But the geological significance of these 

 phenomena becomes most apparent when we seek for the origin of 

 the force. 



We have already seen that the occurrence of the phenomena does 

 not depend upon conditions of temperature or moisture, for they are 

 observed at all seasons of the year, and during all kinds of weather. 

 Nor can it be supposed that such changes would produce a force 

 which should exert itself in only one line of direction. As previously 

 indicated, no doubt such changes often cooperate with the primary 

 power, and by assisting it to overcome resistances, precipitate the 

 explosive movements before they might otherwise have taken place; 

 but that there is a power, which, at times at least, is independent of 

 all such changes, is even more distinctly observable. Nor can the 

 existence of this power be attributed to any peculiarity in the consti- 

 tution of the rocks, for it works in the same way in gneiss and 

 sandstone, in grit and limestone. Nor can chemical or metamorphic 

 changes be considered as the origin, for at the localities mentioned 

 the rocks are less affected by such action than at many other places. 

 Neither can peculiarities of geological structure or of geographical 

 position be assigned as the determining cause; for steeply inclined 



