Vol. 67.] ANNIVERSARY ADDRESS OF THE PRESIDENT. XClii 



restoration of those geographies there is but one unfailing guide, 

 unceasing comparison, at every stage, of the ascertainable geological 

 phenomena of the past with the known geographical phenomena of 

 the present. But, in following that guide, every step must be made 

 with the greatest caution and circumspection. It is not sufficient 

 to recognise alone the fact that the succession of geological systems 

 and formations is representative, on the whole, of geological time ; 

 but we must recognise the fact that each individual formation 

 must be studied as a lithological unit, its local place and limits in 

 time accurately fixed, and its time-equivalent elsewhere determined. 

 In this task we meet at every stage on the one hand with un- 

 expected difficulties, and on the other with unexpected interpretative 

 geographical parallels. This gives to our work the interest of 

 novelty and the charm of unceasing discovery, and to each one 

 of us may come in turn the personal satisfaction of having contri- 

 buted some new factor or some new generalisation to the History 

 of the Earth. 



