92 



VI. Appearance of Life. 



1. Importance of Fossils. 



(a) Development of animal and plant kingdoms. 



(b) Distribution of animals and plants. 



(c) Climatic conditions. 



(d) Distribution of land and water. 



(e) Comparative age of strata. 



2. Conditions for Forming Fossils. 



(a) Remains of plants and animals in water. 



(b) Exclusion of oxygen. 



(c) Deposition of fine sediment. 



3. Forms of Fossils. 



(a) Cast or mold. 



(b) Original material. 



(c) Petrifaction. 



4. Incomplete Life Record. 



(a) I< ew land animals and plants preserved. 



(b) Organisms exposed to oxidation decomposed rapidly. 



(c) Water animals with soft parts leave no trace. 



(d) Fossils destroyed by metamorphism or solution. 



VII. Distribution of Land and Water. 



1. Maps. 



(a) Duplicate maps of North America. 



(b) Indicate supposed areas of land and water during geological 



eras. 



2. Hypothetical maps of North America. 



(a) Archaean era. 



(b) Carboniferous period. 



(c) Cretaceous period. 



(d) Tertiary period. 



(e) Glacial and Champlain periods. 



These maps can be found in geological works by Shaler, Dana, Tarr. 



Children should compare in imagination the life conditions of dif- 

 ferent geological eras and periods with the present. 



They should know that all geological time is divided into four great 

 periods. 



1. Archaean possibly without life. 



2. Paleozoic. 



(a) Cambrian. 



r Trilobites. 



(b) Lower Silurian. 



(c) Upper Silurian. , Fjshes 



(d) Devonian. 



(e) Carboniferous. Amphibians. 



