ON THE ORIGIN OF COAL. 183 



tlian from forty to two hundred and fifty feet ; but 

 they are now covered with sea-deposited strata, 

 from eight hundred to a thousand feet in thick- 

 ness ; hence, the bed of the sea, on which these 

 shells once lived, must have sunk downwards 

 several hundred feet, to allow of the accumulation 

 of the superincumbent strata. What a history of 

 geological changes does the simply constructed 

 coast of Patagonia reveal ! " 



In the early part of this paper, the evidences 

 of periodical subsidences, and periodical rests in 

 those subsidences, as exhibited by the beds of 

 fossil shells, were brought before your notice ; 

 they showed great regularity of motion in the 

 earth's crust, extending during vast periods of 

 time. Is it likely that such a series of phenomena 

 should at once change ? No. — It is much more 

 philosophical to suppose that it continued on 

 during the whole period of the formation of the 

 carboniferous strata, and the successive forests of 

 fossil trees entombed in them, standing on the 

 exact spots where they grew and flourished, to 

 most minds must satisfactorily prove it. The 

 evidences of the periodical states of elevation and 

 repose of the Patagonian coast, are but the 

 reversed action of what has taken place during 



