ON THE ORIGIN OF COAL. 149 



Ibbotson, on the Tertiary and Cretaceous deposits 

 of the Isle of Wight, at the meeting of the British 

 Association, at York, in 1844, showed how it 

 should be applied in measuring the depths of the 

 ancient seas. 



The level of the ocean itself is now assumed 

 by geologists to have been permanent, whatever 

 variations may have taken place in its bottom. 



In the present communication it is the author's 

 desire to direct attention to the constant evidence 

 of subsidences in the bed of the ancient ocean, 

 from the commencement of the protozoic rocks, 

 up to and including the new red sandstone for- 

 mation on the western side of the penine chain, 

 and to point out some of the great epochs of 

 repose which have at intervals of time, in particular 

 places, for a period interrupted such subsidences. 

 Every group of fossiliferous strata offers numerous 

 evidences of subsidence interrupted by periods of 

 rest, but the periods of elevation are not so 

 observable, although it is probable that they 

 must have acted on other parts of the earth's 

 surface to counterbalance such subsidences. But 

 geological works have lately been published 

 wherein the earth's crust is not only assumed to 



