GEOLOGY 141 



of this law a comprehensive science of historic geology would 

 have been impossible. Earth history would have been merely 

 a collection of unconnected local histories with nothing to show 

 the relative place of each local historical unit to the history 

 of the earth as a whole. 



Geological development alone, unaided by the evolution 

 of organic life, cannot supply all the data for the history of 

 earth development as a whole, nor indeed for any particular 

 locality, unless that locality contain unbroken the whole record 

 of geological time. Such a locality is not known to exist. 



Earth development is not progressive. It consists of suc- 

 cessive changes or successive repetitions, and a gap in the 

 record in one locality cannot be supplied from that of an- 

 other locality because of the impossibility of correlating the 

 two. The two cannot be set side by side and adjusted with- 

 out the aid of organic life. The latter is the sole means of 

 placing them in their relative positions in time. Not only 

 that, but the width of a gap in any local history can be deter- 

 mined much more accurately by means of the difference in 

 the stage of development between the organisms on each side 

 of the gap than by any other means. 



During the latter half of the eighteenth century fossils 

 gradually came to be recognized as true organic remains and 

 as the remains of organic beings that lived at a time when 

 the existing land was sea bottom. The next stage in the 

 development was made by an English geologist, William 

 Smith, who discovered that a certain series of beds of rock 

 could be traced entirely across England by means of its fossil 

 remains; that these remained essentially constant throughout 

 that formation, but did not pass upward into overlying forma- 

 mations, nor downward into underlying ones. Smith was 

 able by this discovery to predict the locality from which any 

 particular fossil came, even though he saw it in a distant 

 museum, provided of course that it came from England. It 

 was soon found that this discovery applied not only to the 



