ON GEOLOGICAL TIME. 



{Address delivered before the Geological Society of Glasgow, 

 February 27, 1868.] 



I. A C.KKAT reform in geological speculation 

 seems now to have become necessary. A very 

 earnest effort was made by geologists, at the end 

 of last century, to bring geology within the region 

 of physical science, to emancipate it from the 

 dictation of authority and from dogmatic 

 hypotheses. The necessity for more time to 

 account for geological phenomena than was then 

 generally supposed to be necessary, became 

 apparent to all who studied with candour and with 

 accuracy the phenomena presented by the surface 

 of the earth. About the end of last century, also, 

 physical astronomers made great steps in the 

 theory of the motions of the heavenly bodies, and, 

 among other remarkable propositions, the very 



