REPORT OF MEETINGS FOR 1902 237 



undisturbed position upon highly contorted and probably- 

 reversed rocks of Gala Age. The events which happened 

 in the interval between the time when the one was formed 

 and that when the other first came into existence in its present 

 position, relatively to the unconformable rocks below, may 

 be stated as follows: — 



Time in years. 

 Interval between the Caledonian Old Red 



and the Upper .. .. .. 18,000,000 



Time required for the formation of the 



Caledonian and Orcadian Old Eeds 100,000,000 



Post Silurian denudation of older date than 



the last . . . . . . 24,000,000 



Formation of Silurian (and Lanarkian) 

 Eocks of newer date than the Gala 

 Eocks .. .. .. .. .36,000,000 



Total chronological value of the uncon- 

 formity at the Siccar Poirft — in years 178,000,000 



This is only one of many great unconformities of which the 

 geologist is cognizant. If, therefore, I state that the Upper 

 Old Eed Sandstone of the Siccar Point is itself a rock of 

 high antiquity, dating back to more than four hundred millions 

 of years from our own times, the reader may be less disposed 

 to be incredulous than if I had stated these figures at the 

 outset. 



In concluding this section I will only ask the reader to 

 remember this : — Geology is quite a modern science, recording 

 facts and ideas which are novel to even the educated men 

 of to-day. Astronomy is a science of great antiquity as 

 .such. The astronomers' estimates of celestial distances were 

 for hundreds of years regarded as so much at variance with 

 the views current amongst thoughtful men that it took long 

 before such a statement as, let us say, the distance in miles 

 of the Sun from the Earth was fully realised or admitted to 

 be correct. Still more time was required before people would 

 admit that the astronomers' estimate of the distance of Alpha 

 Centauri, the nearest Star, was true to the facts. 



