66 



THE EAETH. 



volcanic formations ; in other cases rising in enormous 

 quantities through openings at the bottom of the seas, partly 

 filling these up, driving off" the waters, and thus covering 

 many of the coral formations with coatings of sand to a 

 great thickness, raising up others into considerable elevations, 

 and forming hills and fresh tracts of earth. 



During this long period of comparative quiet most of the 

 irregularities on the surface of the earth became worn down, 

 and extensive swamps were produced by partial evaporation 

 of the inland lakes. These swamps were subject to occa- 

 sional inroads of the sea, and at times formed shallow lakes 

 or lagoons ; in these grew the most luxuriant vegetation, 

 gigantic pines, tree-ferns (fig. 18), equisetacse, &c. These 



FIG. 18. FOSSIL TREE FEENS. 



plants, nurtured by a hot and moist climate, acquired a great 

 luxuriance of growth, and must have formed forests of such 



