36 



THE CHAIN OF LIFE. 



l)roduced are so similar that it is oft'»n quite impossible to dis- 

 tinguish them by the naked eye. Like Eozoon, they form the 

 substance of important limestones, and single masses are some- 

 times found as much as three feet in diameter. The Stromato- 

 porce extend through the Silurian into the Devonian. In the 

 Carboniferous they are continued by smaller and more regular 

 organisms of the genus Lofttisia^ and this genus seems to 

 extend without marked change up to the Eocene Tertiary. In 

 modern times I know of no nearer representative than the 

 animal whose skeleton often adheres in red encrusting patches 

 to our specimens of corals, and which is known as Polytrema^ 



Fig. i-^.-^Caunopora planulata. Showing the radiating canals on a weathered 

 surface. Devonian. — After Hall. 



In general structure it is not very far from being a very 

 degenerate kind of Stromatopora. 



It is curious that ' ' the line of succession above stated, the 

 beautiful tubulat'^ wall of Eozoon disappears; and this 



structure see'' ^ the Laurentian, to be for ever divorced 



from the grt aminated Protozoans. It reappears in the 

 Carboniferous, in certain smaller organisms of the typ^ of the 

 Nummulites, or Money-stone Foraminifers, and is continued in 

 this group of smaller and free animals down to the present time. 

 In the Cretaceous and early Tertiary periods, the Foraminifera 



^ Loftusia Columbiana^ Dawson, from British Columbia, is the only 

 Carboniferous species yet known. 



