SUBSIDENCE OF VARIOUS DEPOSITS. 



157 



existence of a vegetable earth or mould, of a soil nearly dry, resting 

 on marine deposits. This bed has been covered by a very tlrck 

 deposit of lacus'trine limestone, and the whole passes under tne 

 green sand which precedes the chalk, and which is of marine for- 

 mation. It is clear, therefore, that there was in those places a cer- 

 tain upheaval of the inferior marine limestone, on which terrestrial 

 plants grew; that subsequently a lake, or a deep estuary, was 

 formed, in which beds of limestone, sand, and clay, were deposited, 

 filled with fluviatile shells, the entire mass being sometimes from 

 200 to 500 yards in thickness. A subsequent upheaval must have 

 lifted the whole to its present level. 



Around the Paris basin, the deposit of marine limestone, worked for build. 

 ing stone, must have been at first uplifted, at various points, above the sea, 

 to be ccfvered by a fresh- water lake in which lacustrine deposits were formed, 

 and among- them the plaster of Paris ; subsequently, it must have been sunk 

 beneath the sea, to be covered by a marine formation, and again uplifted, to 

 be covered by a second fresh- water formation. 



Fig. 251. Impressions of feet of quadrupeds. 



Hundreds of facts of this kind might be cited ; but we will only notice the 

 impressions of feet and tracks of certain quadrupeds (Jig. 251) found at Hess- 



berg, near Hildburghausen, in Saxony, 

 on the faces of certain beds of sand- 

 stone, and the impressions of the feet 

 of various birds, found in the valley of 

 the Connecticut, in the United States, in the 

 same deposits (Jig. 252). These impres. 

 sions show that the soil was in a degree 

 soft, although partly dry, which is proved 

 by the ridges it presents, and that it was 

 out of water ; the sedimentary bed on 

 which these animals walked, is now co- 

 vered by another, which is moulded on 

 these tracks, and afterwards by considera- 

 ble deposits of the same matter which could 

 be formed only under water ; it follows, 

 therefore, that the soil, first uplifted enough 

 to enable terrestrial animals to walk on it, 

 was subsequently sunk to receive all those 

 sedimentary deposits, and afterwards wa 

 Fig. 252. Bird tracks again upheaved to its present position 



14 



