§ 47. SEQUENCE OF GEOLOGICAL CHANGES. 445 



which was gradually consolidated into limestone ; thermal 

 streams, holding flint in solution, percolated the mass, and 

 silicified the submerged trees and plants. 



A further subsidence took place, floods of fresh water 

 overwhelmed the petrified forest, and heaped upon it accu- 

 mulations of detritus, which the streams and rivers had 

 transported from the land. The country traversed by the 

 rivers, like that of the submerged forest, enjoyed a tropical 

 climate, and was clothed with palms, arborescent ferns, and 

 cycadeae ; it was tenanted by gigantic herbivorous and 

 carnivorous reptiles, and its waters abounded in turtles, 

 and various kinds of fishes, crustaceans and mollusca. 

 The bones of the reptiles, the teeth and scales of the fishes, 

 and the stems, leaves, and seed-vessels of the trees and 

 plants, were brought down by the streams, and imbedded 

 in the mud of the delta, beneath which the petrified forest 

 was now buried. 



This state continued for an indefinite period — another 

 change took place — the Country of Reptiles with its inhabi- 

 tants was swept away, and the delta, and the fossil trees 

 with the marine strata oh which they grew, subsided to a 

 great depth, and formed part of the bottom of a profound 

 ocean ; the waters of which teemed with numberless 

 zoophytes, shells, and fishes, of species long since extinct. 

 Periodical intrusions of thermal streams charged with silex, 

 gave rise to layers and veins of nodular and tabular flint, 

 and occasioned the silicification of the organic remains sub- 

 jected to their influence. 



This epoch, which was of long duration, was succeeded 

 by elevatory movements, by which the bottom of the deep 

 was broken up, and large areas were slowly upheaved ; 

 and as the elevation continued, the deposits which had 

 accumulated in the depths of the ocean approached the 

 surface, and were exposed to the action of the waves. 

 These masses of cretaceous strata now began to suffer 



