340 THE BOOK OF THE ANIMAL KINGDOM 



are kinds of life-forms which, in the procession of life, have fallen 

 out by the way and perished. Their remains, as found in the 

 earth's strata, are known as fossils (literally, something dug up). The 

 study of these remains, or fossils, is called Palaeontology, which 

 means the science of ancient life. 



It must be borne in mind that our earth is very old and has been 

 inhabited by living creatures of various kinds for aeons. Man is 

 quite a recent arrival, and has been fittingly called "the crown of 

 creation." The first living forms were characterized by simplicity 

 of organization, and as the world has grown older there has been 

 a remarkable succession of life-forms, exhibiting more and more 

 elaborate developments. The simplest life-forms are found in the 

 oldest sedimentary rocks, and as strata have succeeded strata so 

 have the creatures peculiar to them betrayed variations and greater 

 complexity. 



Generally speaking, there are two kinds of rocks which enter 

 into the composition of the earth as we know it to-day — the igneous, 

 or fire-formed rocks, and the sedimentary or deposited rocks. The 

 sedimentary rocks are made up in their first origin of the wear and 

 tear of igneous rocks, and have been deposited in the form of mud 

 and sand; they also consist of limestones which in some instances 

 have been chemically precipitated, but in most cases are made up of 

 the calcareous remains of occupants of seas and lakes. Naturally, we 

 do not look for fossil remains in the igneous rocks ; it is to sedimen- 

 tary deposits, or stratified rocks, that we must turn if we would find 

 vestiges of ancient life-forms. The oldest strata are, of course, the 

 lowest and most interior of the sedimentary deposits, and had the 

 succession of strata laid above them been evenly deposited, and left 

 undisturbed, we should know little or nothing of them ; indeed, they 

 would be many thousands of feet below the present surface and 

 beyond our reach. Fortunately, many forces have been at work by 

 which even the ol4est strata have been exposed. Later deposits have 

 been washed away; streams of water have cut through strata and 

 made their succession and content's evident, and there have been earth 

 movements, causing faulting by which recent deposits are lowered 

 and older ones raised. In many instances strata have been turned 

 on edge, and as one walks over the ground where this phenomenon 

 has taken place, one progresses across the upturned edges of strati- 

 fications which are the work of ages upon ages. There are numerous 

 cases in which rocks have actually been folded by earth movement, 



