ON THE ORIGIN OF COAL. 193 



All these instances prove the existence of land 

 covered by water, but no dry land, and confirm 

 Brongniart's opinion, formed from the examination 

 of Stigmaria, that the Sigillaria was an aquatic 

 plant. 



Sufiicient evidence has not been adduced to 

 prove that the various other plants found in the 

 coal measures were grown on the places where 

 they are now found, for we have not been able to 

 detect their roots in situ. This remains to be done. 



With respect to the Sigillaria, there can scarcely 

 be a doubt but that it grew in water, on the 

 deposits where it is now discovered, and that it 

 is the plant which in a great measure contributed 

 to the formation of our valuable beds of Coal. 



In this, my first attempt to connect the currents 

 which existed during the deposition of the Coal 

 measures, with the rate of subsidence of a portion 

 of the earth's crust, I have adduced evidence to 

 prove that the subsidences during the period under 

 review were of such a character, in general, as to 

 cause slow and gradual movements, similar to what 

 Mr. Babbage avers would arise from the contrac- 

 tion of the earth's crust by the radiation of heat, 

 c c 



