164 DYNAMICAL GEOLOGY. 



interior of the earth of a general liquid subject to tides. 

 But the argument is evidently valueless, for any force 

 tending to lift and break up the crust of the earth would 

 be assisted by the gravitation or lifting power of the 

 moon in passing the meridian, and this lifting power 

 would be greatest at the times indicated above. Suppose, 

 then, an interior force, tending to elevate and break the 

 crust, constantly increasing but resisted by the rigidity of 

 the crust : it is evident that, when the two forces are 

 nearly balanced, the lifting force of the passing moon 

 might well determine the moment of fracture. The 

 moon does not produce the earthquake, but only deter- 

 mines the moment of its occurrence only adds the last 

 feather that breaks the earners back. 



Connection with Season and Weather. By the 

 discussion of the times of occurrence of a large number of 

 earthquakes it is found that they are a little more fre- 

 quent in winter than in summer. No cause for this is 

 known. 



Again : It is a popular belief that the occurrence is 

 usually associated with an oppressive feeling of the atmos- 

 phere, or with storms. These meteorological phenomena 

 are usually attended with a low condition of the barome- 

 ter. Now, a low barometer means diminished pressure of 

 the atmosphere, and this, again, might determine the 

 moment of fracture of the crust. But this, like the 

 attraction of the moon, must be regarded, not as the 

 cause of the earthquake (which undoubtedly lies wholly 

 within the earth itself), but only as sometimes determin- 

 ing the moment of its occurrence. 



SECTION III. GRADUAL OSCILLATIONS OF THE EARTH- 

 CRUST. 



The movements included under this head are on a 

 grand scale, perhaps affecting whole continents, but usu- 



