RETROSPECT. 405 



portion of the bed of the Oolitic sea was elevated 

 above the waters, and constituted an island 

 clothed with pine-forests, and cycadeous plants.* 



II. The Wealden Epoch. — The country with 

 its pine -forests was gradually submerged, and 

 formed the beds of estuaries and bays, into which 

 land floods, loaded with sedimentary detritus, depo- 

 sited mud, silt, and sand, abounding in the remains 

 of freshwater mollusks and crustaceans ; in which, 

 from occasional irruptions of the sea, were inter- 

 calated layers of oysters, and estuarine shells. 

 Bones and teeth of terrestrial reptiles, and of river 

 fishes, with stems and fragments of coniferous wood, 

 were also drifted into the estuaries and bays by the 

 streams and rivers. -j- The gradual subsidence of 

 the sea-bottom covered by these freshwater beds 

 continued, and the sediments accpuired an exclu- 

 sively fluviatile character, till at length the accu- 

 mulated deposits of avast river formed an extensive 

 delta, many hundred feet in thickness, upon the 

 inferior strata. The imbedded organic remains 

 attest, that throughout this epoch the fauna and 

 flora of the country through which the river 

 flowed, corresponded with those of the islands and 

 continents of the Oolitic period.^ 



* Evidence : the Fossil Forest of Portland, &c. p. 395. 



t Evidence: the Purheck strata, p. 354. 



% Evidence: the Wealden strata and fossils, p. 332. 



