224 PLANT-LIFE 



there is evidence of a grand procession of life-forms, and, 

 for purposes of classification, and as an aid to intelligent 

 compreliension, the story of that procession is treated 

 of as involving four great Eras : 



1. Eozoic (Gr. eos, dawn; zoe, life). 



2. PAL^aiozoic (Gr. palaios, ancient; and zoe). 



3. Mesozoic (Gr. mesos, middle; and zoe). 

 i. Cainozoic (Gr. Jcainos, recent; and zoe). 



The Eozoic rocks are as a book of one long chapter, 

 which we call the Archaean Period. It has been esti- 

 mated that the strata of this Period are not less than 

 50,000 feet in thickness. The immense time involved 

 in their deposition staggers the imagination, but we may 

 rest assured that in the progress of that time there was 

 both a coming and going of both plant and animal 

 forms. The lower rocks of the Period consist of igneous 

 and sedimentary deposits, such as the gneisses and 

 schists of the Scottish Highlands, which have been so 

 changed or metamorphosed by stress of earth-movement 

 and other influences that their original constituents 

 have been altered in character. To the fossil-hunter 

 these rocks yield no prizes ; he searches in them in vain 

 for vestige of animal or plant; yet they represent an 

 Era of the dawn of life-forms. But those forms, mayhap, 

 were so simple and perishable that they could not 

 become fossilized, or if they did become so, the rocks 

 containing them have since been subjected to such 

 alteration that the remains are not now recognizable. 

 The life and landscape of the remote times represented 

 by these rocks is left to the imagination. In the upper 

 series of rocks of the Archaean Period there are slight 

 traces of life; some seams of limestone amongst them 



