- ORGANIC EVOLUTION 59 



at the bottom of the sea, and have, hence, all 

 been formed since the condensation of the oceans. 

 They have been formed out of the detritus of 

 continents brought down by the rivers and the 

 accumulated remains of animal and vegetal forms 

 which have slowly settled down through the waters. 

 They are the successive cemeteries of the dead past. 

 Such rocks are now forming over the floors of all 

 oceans forming just as they have formed through- 

 out the long eons of geological history. Along 

 the axes of ancient mountains and in deep-cut 

 canyons the rock layers are exposed to a thickness 

 of thousands of feet, in some cases thirty or forty 

 thousand feet. Here they lie, piled up, one on 

 top of another, the great, broad pages upon which 

 are written the long, dark story of our planet. It 

 is the mightiest and most everlasting of all annals 

 the autobiography of a world. It is possible, by 

 studying these rock records, to know not only the 

 kind of life that lived in each age, but a good deal ' 

 regarding the conditions in which that life lived 

 and passed away. Just as the naturalist is able, 

 from a single bone of an unknown animal, to 

 reconstruct the entire animal and to infer some- 

 thing of its surroundings and habits of life, and as 

 the archeologist, by going back to the graves of 

 deceased races and digging up the dust upon 

 which these races wrought, is able to tell much 

 of their history and characteristics, so the geologist, 

 by studying the bones of those more distant 

 civilisations, the civilisations sandwiched among 

 the fossiliferous rocks, is able to know, not only 



