Handbook of Paleontology 197 



also the Age of Primitive Invertebrates. The two eras 



are separated by a widespread unconformity and are 



classified as follows : 



Ep-Proterozoic Interval and Peneplanation of Continents 



f Late Proterozoic (Keweenawan series) 

 {Break in Record) ,...,. 

 Proterozoic \ Middle Proterozoic f Animikian series 

 (Former Life) \ Unconformity _ \ Huronian series 



[Lower Proterozoic (Sudburian series) 



Ep-Archeozoic Interval and Peneplanation of Continents 

 f Laurentian granites 

 Archeozoic J ? Grenville series (May prove to be 



(Ancient Life) ] Proterozoic (Huronian) 



[ Keewatin — Coutchiching series 



Beginning of earth history 

 Geologists have not as yet seen the original foundation 

 upon which the Archeozoic rocks rest nor have they any 

 evidence as to what took place in earliest Archeozoic 

 time. It is thought that the surface of the earth in earli- 

 est geologic times must have been made up of igneous 

 rocks, probably mostly granites. With the appearance of 

 rains erosion of the rocks began and the first sediments 

 were deposited - — sandstones and mudstones. The first 

 limestones were probably chemical but later were depos- 

 ited through the agency of organisms. No rocks are 

 more complex than those of the Archeozoic era. They 

 are known as the basement complex: first, because they 

 are the oldest rocks of which we have any present knowl- 

 edge and, as far as known, underlie all the younger rocks 

 of the earth's crust; second, because of their highly 

 altered, complex, present nature. None of the forma- 

 tions are in their original condition. They have been 

 uncovered in regions where there has been repeated uplift 

 and erosion and these can be studied. The greatest ex- 



