CHAPTER III. 



THE AGE OF INVERTEBRATES OF THE SEA. 



IF the middle portion of the Laurentian age was really a time 

 of exuberant and abounding life, either this met with 

 strange reverses in succeeding periods, or the conditions of 

 preservation have been such as to prevent us from tracing its 

 onward history. Certain it is, that according to present ap- 

 pearances we have a new beginning in the Cambrian, which 

 introduces the great Paljeozoic age, and few links of connection 

 are known between this and the previous Eozoic. 



At the beginning of the Palaeozoic we have reason to be- 

 lieve that our continents were slowly subsiding under the sea, 

 after a period of general continental elevation which was con- 

 sequent on the crumplin.s: of the earth's crust at the close of 

 the Eozoic ; and on the new sea-bottoms formed by this subsi- 

 dence came in, slowly at first, but in ever-increasing swarms, 

 the abundant and varied life of the early Palaeozoic. 



In the oldest portion of the Cambrian series in Wales, Hicks 

 has catalogued species of no less than seventeen genera, em- 

 bracing Crustaceans, the representatives of our crabs and lob- 

 sters, bivalve and univalve shell-fishes of different types, worms, 

 sea-stars, zoophytes, and sponges. If we could have walked 

 on the shores of the old Cambrian sea, or cast our dredge or 

 trawl into its depths, we should have found representatives of 

 most of the humbler forms of sea life still extant, though of 



