FOSSILS AND THEIR TEACHINGS. 69 



LESSON XIII. 



FOSSILS AND THEIR TEACHINGS. 



123-125. Earth development. 126. Animal Kingdom. 127. Life- 

 less Time. 128. Ancient Time. 129. Silurian: Thallogens, In- 

 vertebrates ; Acrogens, Fishes. 130. Devonian: Gymnosperms, Fishes, 

 Insects. 131. Carhoniferous : Tree-Ferns, Horsetails, Club-Mosses. 

 182. Middle Time. 133. TViressic ararf Jwrassic .• Cycads, Endogens, 

 Reptiles, Reptilian Birds, Pouched Mammals. 134. Cretaceous : Exo- 

 gens, Wader-Birds. 135. Modekn Time. 186. Tertiary: Modern 

 Plants and Animals. 137-140. Quaternary: Man. 141. Natural 

 Selection. 



123. "In the beginning the earth was without form and void," — a 

 chaotic nebulous mass (supposed to have been 800,000 times its present 

 size), which was slowly condensed into a liquid ball of molten minerals. 

 As its surface cooled, a rocky crust was formed ; this, on account of 

 commotions within the mass, was thrust up and folded in various ways. 

 The vapors became seas ; these seas wore away the surface of the first 

 rocks and formed layers ; upheavals and depressions made lakes and 

 rivers; finer deposits made soil. The ci-ust of the earth, the best geolo- 

 gists presume, has an average thickness of 25 miles, — less than ^^ of 

 its diameter, and thinner in comparison than an egg-shell. 



124. Earih^development has four divisions of Time (see Table facing 

 Lesson XIII.) : 



/. lAfeless Time, or Azoic (Gr. re, wanting, zoe, life). Without 

 plants or animals. 



//. Ancient Time, or Palaeozoic (Gr. palaios, ancient). Plants and 

 animals prefiguring modern types but diflferent from them. 



///. Middle Time, or Mesozoic (Gr. rnesos, middle). Plants and 

 animals more like modern types. 



IV. Modern Time, or Cenozoic (Gr. kainos, modern). Plants and 

 animals as they are to-day. 



125. Giving to each period its relative age as counted from the time 

 required to make modern deposits of stone, mud, etc., the proportion 

 is 4, 12, 3, 1. The age of the earth is reckoned to be 60 millions of 

 years. We have, then, for Lifeless Time 12 millions ; Ancient Time, 

 36 millions ; Middle Time, 9 millions ; Modern Time, 3 millions. 



126. The Animal Kingdom (Zoology), like Botany, has two Series : 

 Series I. Invertebrates, without spinal column. Reproduction 



single, dual, alternate. Multiplication by gemmation (producing 

 gems or oflFsliOots). Four classes : 

 .1. Protozoa (Numraulites, Sea-Jelly) ; as simple as protophytes. 



2. Radiates (Sea-Fir, Star-fish, Coral) ; plant-like. 



3. Mollushs (Oyster, Clam, Snail, Cuttle-fish) ; soft-bodied. 



4. Articulates (Worm, Crab, Insect) ; jointed. 



