readily. This may be explained by assuming that the Creator annihilated all life at the close 

 of each period and then created new forms, closely resembling the old, by the method of 

 direct, or spzcial creation. It would be exactly as reasonable to suppose that he annihilated 

 the earth itself at the same time creating it anew, because we find it somewhat different dur- 

 ing each period. Just as the earth was slowly changed by the agencies described in chapter 

 I, so scientists believe that the forms of plants and animals of one period were gradually 

 modified into those of the next period, as rapidly as newer and better environments were pre- 

 pared to receive them. 



a. Cambrian period. Animal life during this period was abundant and varied, but con- 

 fined to the invertebrates. The dominant typs was the crustacean, to-day represented by the 

 lobsters, crayfish atid crabs. Marine plant lite must have existed, but is known only by a few 

 obscure imprints of sea weed. The continents and islands were of limited size and no traces 

 of land life have yet been found. 



b. Silurian period. (Ordovician and Silurian.) Upheaval of portions of the Cambrian 

 sea bottom increased the land areas somewhat, but the sea was still of wide extent. The 

 group of mollusks, represented to-day by the clam, oyster, snails and nautilus, became the 

 dominant type. Fragments of their shells, mingled with the hard parts of corals, crinoids, 

 etc., gave rise to great beds of limestone. Remains of marine plants are surprisingly scarce 

 and related to the algae of to-day. Land insects have been found and traces of ferns. The 

 concentration of inland seas by evaporation gave rise to beds of salt over certain areas. 



c. Devonian period. During the Silurian and at its close much more land was added to 

 the continents. This land was forested with trees of a primitive type, with an undergrowth 

 of ferns and rushes. Insect and land mollusks are known to have lived. In the water 

 especially marine, the group of plants known as rhizocarps flourished in countless numbers. 

 Their spores accumulated in the mud rocks (shales) and gave rise to much oil and gas. The 

 most remarkable advance was in the animal life of the ocean and bodies of fresh water. The 

 lowest class of backboned animals the fishes had come into great prominence from their 

 numbers and size. These are vertebrates adapted to an aquatic mode of life by gills and fins. 

 They are usually covered with scales or plates, have a single auricle and ventricle and are 

 cold blooded. 



d. Carboniferous period. (Carboniferous and Permian). A further great expansion of 

 the laud occurred, much of it standing near sea level; a warm, moist climate extended well 

 toward the poles and the air was highly charged with carbon-dioxide gas. In many regions 

 conditions were most favorable for the growth of moisture loving plants. The lycopods, 

 represented today by the ground-pine, shot up into magnificant forest trees, mingled with 

 which were tree ferns and gigantic rushes. Much vegetable matter accumulated in the 

 swamps where, out of contact with oxygen, under the pressure of later deposits, with some 

 internal heat of the earth, it was finally converted into coal. Dr. Winchell poetically referred 

 to this substance as "Solidified sunlight." The fishes, modified from the Devonian forms, were 

 rulers of the sea, preying upon one another and upon the invertebrates. In the fresh waters 

 of the land a higher type of vertebrate had appeared; the amphibian, represented to-day by 

 the mad-puppies, salamanders, frogs and toads. They were numerous and grew to much 

 larger size than at present. Can you find any reason why? This class of vertebrates has 

 typically a smooth skin and no claws and breathes, in the adult stage by lungs. Fore and 

 hind limbs are present. They are cold blooded and have two auricles and one ventricle. 



4. MESOZOIC ERA. During this "middle life" of the earth's history there occurred a 

 marked advance in the continents and their surface features, as well as in the plant and 

 animal life. It is usually divided into three periods which may not be here recognized. The 

 dominant type of plants was the cycad, a tree which combined characteristics of the conifers, 

 the palms and the ferns, only a few representatives of which are still living in the tropics. 

 The next higher group of vertebrates; the reptile, had appeared and in enormous numbers 

 and almost unbelievable size dominated the seas, land, trees and air. The reptile is a tailed, 

 cold blooded vertebrate, with fore and hind limbs, generally present, covered with plates or 

 scales and provided with claws. It breathes by lungs and has two incompletely separated 

 ventricles (lizards, crocodiles, turtles, snakes, etc.). During this era conditions in the sea were 



