156 Sioux City Academy of Science and Letters. 



few uncertain plants. The first vertebrates have so far 

 been found near the close of the Upper Silurian age, and 

 these are all fishes. None of them have yet been found 

 in America, but only in Europe. Dana says the first cer- 

 tain land plants have been found in the closing part of 

 the Lower Silurian age, and that the land of the Tren- 

 ton period had its Ferns and Lycopods. Such fossils as 

 these indicate the possible existence of terrestrial articu- 

 lates. 



The next, or Devonian age, has been called the age 

 of fishes from the abundance of the remains of these 

 animals that have been found in its rocks. During this 

 age, terrestrial plants appear in profusion for the first 

 time. They are of higher orders than any which have 

 been found in rocks of an earlier age. They are Lyco- 

 pods, or ground pines, Conifers and Ferns. 



We next reach the Carboniferous, or coal making 

 age. This age began, both in America and Europe, with 

 a marine period and closed with one. During the mid- 

 dle part of this age were laid down the great beds of 

 coal that are found in all parts of the world. This was 

 truly a time of preparation for the higher life that should 

 appear at a later time. There were two distinct lines of 

 development carried forward together, one caused by the 

 other. The physical condition of the inorganic world 

 was well suited to a wonderful growth of vegetable life. 

 The air was yet heavy with its excess of carbonic acid, 

 thus furnishing the needed nutriment for the wonderful 

 plant life which grew so luxuriantly. The crust of the 

 earth was yet unsettled and its oscillations up and down 

 alternately submerged and then uncovered the land sur- 

 face. In this way were covered up and preserved the 

 remains of that rank vegetation, to serve us of this later 

 day as coal. These vast deposits thus absorbed and 

 stored up as carbon the excess of carbonic acid and puri- 

 fied the atmosphere, thus making possible higher forms 

 of life. 



Geologists have divided the rocky strata of the past 

 into separate ages, for convenience of study and descrip- 

 tion, and have given them descriptive names. They have 

 called the largest divisions Times, and have named the 

 first one Archean Time. The second grrand division is 



