20 a. BLYTT. [NO. t 



The eruptions are separated by shorter or longer periods of repose. 

 The basalt beds are separated by sedimentary layers. Earth- 

 quakes are a consequence of accumulated strain to which the 

 crust suddenly yields. All this indicates that the crust of the 

 Earth does not immediately accomodate itself to the forces, but 

 that it yields first when the steadily increasing strain has reached 

 a certain point. It appears, still further, to proceed from 

 geological investigations, that there are periods in the history 

 of the Earth when the changes occur on a larger scale than 

 usual. In his Textbook previously mentioned (p. 197—198) A. 

 Geikie speaks of the great eruptive masses, fissure eruptions, 

 that have taken place, both in the Old and New Worlds, in 

 which melted masses were projected from numerous rents and 

 covered thousands of square miles. Modern volcanicity appears 

 slight compared with those gigantic eruptions. 



We will now pass on to examine whether these changes in 

 the form of the Earth may possibly stand in any relation to the 

 periodical change in the eccentricity of the orbit. 



We begin with the assumption that Thomson and Tail speak 

 correctly, when they state that the tidal-wave is the most im- 

 portant of the forces, that contribute to alter the length of 

 the sidereal day. But along with the oceanic tidal-wave acts 

 the internal friction, „the bodily tides" assumed by Darwin. 

 Both are of course dependent on the lunar and solar distance, 

 and we must therefore investigate whether the tidal action of 

 these b 0dies on the Earth changes with the eccentricity of the 

 fht l' 8 £ * Pr ° CeedS fr ° m Da ™™' s investigations that 

 the lunar tides in ancient times, long passed away, must have 

 been much greater than now. I pass that h because that 



^IIT "I ^ ° f the ~icity of the Earth's 



ha the d^° m / 6 Peri ° d ' gGOl « speaking. As I thought 

 er ap S h ^ ° f ^ *™ » ^ eccentricity rig* 



ST o H 8 °n ge ° l0giCal importance ' 1 insulted H. Q+ 



