102 SLOW AND PROGRESSIVE SUBSIDENCE. 



lability of the seas, by acknowledging that the solid surface of our 

 planet is susceptible of elevations, depressions, and all kinds of 

 disturbances. 



The slow upheaval of Sweden has already been noticed (p. 20). 



8. Slow and progressive subsidence. There is no doubt that, 

 for four centuries past, the western coast of Greenland is continu- 

 ally sinking, through an extent of two hundred leagues north and 

 south ; ancient buildings, both on the low islands and on the con- 

 tinent, have been gradually submerged ; and it has been frequently 

 necessary to move various establishments built near the shore, 

 farther inland. Subsidence of certain islands in the South Seas has 

 been indicated ; but in those places, so rarely visited by geologists, 

 the facts are not yet clearly established. 



9. General conclusion. It must now appear to be well estab- 

 lished, that earthquakes are capable of producing great modifica- 

 tions of the earth's surface, since, within our times, vast tracts of 

 country have been elevated sensibly above the level of the sea. It 

 is not less evident there is a slow power in operation, in virtue of 

 which, different parts of our continents may also be successively 

 raised ; and that it also produces gradual sinkings as well as sud- 

 den subsidences, which are doubtless correlative phenomena. 



All these circumstances, however remarkable, are, nevertheless, 

 not very astonishing, when we reflect on the enormous dispropor- 

 tion which exists between the thickness of the solid crust of the 

 globe, and the mass of melted matter it envelopes. Is it surprising 

 that such a crust, a mere rind, relatively almost as thin as a coating 

 of gold-leaf on an orange, should be disturbed.in every manner by 

 die least movement of the subjacent mass, particularly if we beai 

 in mind that similar movements doubtlessly have been taking 

 place ever since the first pellicle was consolidated on the surface, 

 and all the successive crusts must have been rent in every direc- 

 tion, and therefore their mass could not afford the resistance of a 

 continuous envelope ? 



VOLCANIC PHENOMENA. 



10. General notion Erphsion Eruption. Volcanic pheno- 

 mena are closely connected with earthquakes; they are, in a 

 manner, the final results of them. When, by the shaking and ele- 

 vation of the ground, the terrestrial crust is deeply broken, a tem- 

 porary or permanent communication is established between the 

 interior and exterior of the globe, through which various kinds of 

 matter are disengaged from the bosom offhe earth. Through the 

 crevices escape gases of different kinds, waters hot or cold, simple 



8. i there any evidence of the slow and gradual subsidence of land? 



9. Why is it believed that earthquakes modify the earth's surface ? 



10. What are volcanic phenomena? Give some instances of volcanic 

 phenomena. 



