FOSSIL INFUSORIA. 



certain vegetation : that then it was again submerged, either by- 

 fresh water or by the sea, receiving during an indefinite period 

 another stratum, either with fluvial and lacustrine remains or 

 with marine deposits, as the case might be ; that subsequently it 

 was again upheaved, and again became the theatre of animal and 

 vegetable life upon dry land, and so on. 



180. The Portland dirt-beds, already described, prove the 

 existence there, at remote epochs of the globe, of vegetable soil on 

 a land nearly if not altogether dry, beneath which lay a stratum 

 of marine deposits. It follows, therefore, that before this epoch, 

 and before the deposition of the dirt-bed itself with the remains 

 contained on it, that part of the land must have been submerged 

 by the ocean, and that being upheaved, it afterwards became the 

 theatre of animal and vegetable life, such as we find deposited in 



Fig. 107. Fossil infusoria. 



a. Desmidium apiculosum. 

 6. Euastrum verrucosum. 



c. Xanthidium ramosum. 



d. Peridinium pyrophorum. 



e. Gomphouema lanceolata. 

 /. Hemanthidium arcus. 



g. Piunularia dactylus. 



h. Navicula viridis. 



i. Actinocyclus senarius. 



j. Pixidula prisca. 



k. Galliouella distans. 



I. Syuedra ulna. 



in. Bacillaria vulgaris. 



n. Spicula spongiaria. 



the dirt-beds. Over the dirt-beds are thick lacustrine deposits of 

 limestone, which lie under the green sandstone, which latter is 

 itself overlaid by the chalk, this latter being evidently a marine 

 formation. Let us see, then, what a curious succession of phe- 

 nomena is here indicated. The lower marine strata of limestone 

 was first upheaved, and, becoming dry land, was the theatre 

 of rich terrestrial vegetation. It was then submerged by fresh 

 water, and was the place of a lake or deep estuary, in which 

 were formed the strata of limestone, sand, and clay, filled with 

 fluviatile shells, forming a stratum, which from actual observation 

 appears to have a thickness of from seven hundred to a thousand 

 feet. Later still, this was covered by the sea, and marine deposits 

 of green sandstone and chalk were formed upon it, which, at 



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