34 GEOLOGICAL HISTORY. [CH. 



I. Archaean. 



"Men can do nothing without the make-believe of a beginning." 



George Eliot. 



There is perhaps no problem at once so difficult and so full 

 of interest to the student of the Earth's history, as the interpre- 

 tation of the fragmentary records of the opening stages in 

 geological and organic evolution. In tracing the growth and 

 development of the human race, it becomes increasingly 

 difficult to discover and decipher written documents as we 

 penetrate farther back towards the beginning of the historical 

 period ; the records are usually incomplete and fragmentary, or 

 rendered illegible by the superposed writings of a later date. So 

 in the records of the rocks, as we pass beyond the oldest strata in 

 which clearly preserved fossils are met with, we come to older 

 rocks which afford either no data as to the period in which they 

 were formed, or like the palimpsest, with its original characters 

 almost obliterated by a late MS., the older portions of the 

 Earth's crust have been used and re-used in the rock-building 

 of later ages. In the first place, it is exceedingly difficult to 

 determine with any certainty v/hat rocks may be regarded as 

 trustworthy fragments of a primaeval land. Throughout the 

 geological eras the Earth's surface has been subjected to 

 foldings and wrinklings, volcanic activity has been almost 

 unceasing, and there is abundant evidence to show how the 

 original characters of both igneous and sedimentary rocks may 

 be entirely effaced by the operation of chemical and physical 

 forces. It was formerly held that coarsely crystalline rocks 

 such as granite are the oldest portions of the crust, but 

 modern geology has conclusively proved that many of the 

 so-called fundamental masses of rock are merely piles of ancient 

 sediments which have been subjected to the repeated operation 

 of powerful physical and chemical forces, and have undergone a 

 complete rearrangement of their substance. As the result of 

 more detailed investigations, many regions formerly supposed 

 to consist of the foundation stones of the Earth's crust, are 

 now known to have been centres of volcanic disturbance and 



