302 GEOLOGY. 



for under this hypothesis the land was still barren and its waters were 

 wholly sterile so far as food for animals was concerned. Besides, on 

 account of the unprotected nature of the land surface, the wash was 

 unrestrained and the waters were doubtless uncommonly silty. As 

 a result, the sea waters about the borders of the land were at once 

 sterile and muddy, and hence uninviting to most marine animals. 

 It was only as the plants spread to the shores and crept over the land 

 that the shore waters became clear and enriched in organic material. 

 When at length vegetation made the shores and shallow waters con- 

 genial homes for animals, they are thought to have planted them- 

 selves there and to have evolved types adapted to that environment 

 with relative rapidity. 



The second hypothesis. — The other suggestion involves an opposite 

 point of origin and an opposite direction of distribution. It assumes 

 that the first forms of life were simple plants that originated in the 

 land waters. In this, appeal is made to the observation of botanists 

 that the fresh-water plants are of more germinal and plastic types 

 than the marine plants and are apparently better suited to differentiate 

 into the present rich and varied vegetable kingdom. They were better 

 situated for this since the great differentiations of the vegetable king- 

 dom have taken place chiefly on the land. This hypothesis further 

 assumes that the early animals, to a greater or less degree, had their 

 origin in the same waters, and like the plants on which they were depend- 

 ent spread thence to the sea and out upon the land. It is conceived 

 that there might be considerable development of the aquatic forms 

 of animal life, such as the fishes, 1 mollusks, 2 crustaceans, etc., in the 

 land waters before they became denizens of the seas, and their appear- 

 ance in the latter might be at some rather advanced stage of their 

 evolution and hence be seemingly sudden. As has been noted, it was 

 only after the ocean waters were plentifully enriched in vegetable 

 matter that the stationary forms of marine life could be sufficiently 

 supplied with food. This enrichment, however, does not necessarily 

 imply a very great period, geologically speaking. 



It is doubtful whether either of these suggestive hypotheses recog- 



l T. C. Chamberlin, On the Habitat of the Early Vertebrates, Jour, of Geol., 

 Vol. VIII, 1900. 



2 F. W. Sardeson, The Phylogenic Stage of the Cambrian Gastropoda, Jour, of 

 Geol., Vol. XI, No. 5, 1903. 



