CHAPTER III. 



. GEOLOGICAL HISTORY. 



"But how can we question dumb rocks whose speech is not clear i?" 



In attempting to sketch in briefest outline the geological 

 history of the Earth, the most important object to keep in 

 view is that of reproducing as far as possible the broad 

 features of the successive stages in the building of the Earth's 

 crust. It is obviously impossible to go into any details of 

 description, or to closely follow the evolution of the present 

 continents; at most, we can only refer to such facts as may 

 serve as an introduction of the elements of stratigraphical 

 geology to non-geological readers. For a fuller treatment of 

 the subject reference must be made to special treatises on 

 geology. 



For the sake of convenience, it is customary in strati- 

 graphical geology as also in biology, to make use of our 

 imperfect knowledge as an aid to classification. If we possessed 

 complete records of the Earth's history, we should have an 

 unbroken sequence, not merely of the various forms of life 

 that ever existed, but of the different kinds of rocks formed 

 in the successive ages of past time. As gaps exist in the 

 chain of life, so also do we find considerable breaks in the 

 sequence of strata which have been formed since the beginning 

 of geologic time. The danger as well as the convenience of 

 artificial classification must be kept in view. This has been 



1 Old Persian writer, quoted by E. G. Browne in A Year among the Persians, 

 p. 220, London, 1893, 



