1889.J THE DISPLACEMENT OE BEACH-LINES 81 



In examining the geological formations, we find everywhere 

 great breaks in the series of beds. In the Tertiary buildings 

 we see frequent alternations of fresh-water littoral and sub- 

 littcral beds, showing only inconsiderable displacements of the 

 beach-lines. After such a series, corresponding to more or less 

 geological stages, a break occurs, which may often represent seve- 

 ral hundred thousands of years. These breaks commonly show, that 

 the basin was lifted above the sea, and that sedimentation become 

 stopped. These greater upheavals were caused by strains accu- 

 mulated through very long periods. Before this great strain 

 was relieved, the basin was a weak part of the crust and was 

 strained almost to the limit of its elasticity. Slight forces were 

 then sufficient to produce dislocations. Small changes in the 

 magnitude of these forces were sufficient to cause small 

 periodical displacements and intervals of repose. At last 

 the great strain is relieved by a greater upheaval, and the 

 basin is lifted above the sea. And as we have no proof to the 

 contrary, it is permissible to suppose that a long period of repose 

 flowed after the great upheaval. The uplifted basin could now 

 undisturbed by earth movements for many hundred thousands 

 of years. But by the lengthening of the sidereal day fresh strain 

 ^cumulates. And the strain increases, as long as no displace- 

 ments take place. The sea in higher latitudes rises slowly but 

 ^interruptedly. After a long time the sea again inundates 

 ! 6 basm - Tllere is reason to believe that the crust, in the 

 P*en place, is now again strained almost to the limit of its elasti- 

 as it has now again, in relation to the surface of the 

 *cean, the same distance from the earth's centre as it had be- 

 the last greater upheaval. It is, then, reasonable to sup- 

 *> that similar slight displacements will begin anew, and that 

 ^ another greater upheaval will take place, 

 vide b dlSplaCements of the beach-lines which enable us to di- 

 loetl e ^ e6n geol °2 ical sta S es > were only slight and probably 



They were 



not contemporaneous everywher 



^thongh the forces were active at different times in different places. 

 he Present time, some parts of the crust are weaker and 



