356 THE WOULD. 



noes, and the effects produced by their erupti-ms. When we bear 

 iu mind that during the earlier periods of the earth's existence, 

 volcanic action was much more general and severe than at pre- 

 sent, we will be at no loss for a sufficient cause to produce most ' 

 of the upheavings, and contortions of strata, observed on our 

 globe. In some parts of the world, whole districts are composed 

 of extinct volcanoes, which even yet have not wholly ceased to 

 emit deleterious gasses, and the traces of their former and pow- 

 erful action are seen in every country. 



We have not discussed at all, the causes which produce volca- 

 nic eruptions ; these are not yet satisfactorily determined ; and a 

 great diversity of opinion still exists among philosophers. It will 

 be seen upon referring to the diagram, (page 178), that the com- 

 parative height of the loftiest mountains, is but as a minute grain 

 of sand on a large globe, and that such slight changes from the 

 general level of the surface may be produced by causes compara- 

 tively small. 



