THE HISTORY OF LIFE 147 



more constant than the trees. Not only this, but the 

 mammals have progressed along definite lines, so that 

 the different members of the horse group, for example, 

 form a sequence which is readily appreciated. Given the 

 key to this development, increase in size, reduction 

 in the number of toes, and so forth, any one having 

 the fossils before him .could arrange them in the proper 

 order. The oysters, on the other hand, have, as it were, 

 shuffled their characteristics, producing a multitude of 

 species without any distinct advance. Consequently, 

 though the species of oysters are extremely useful for 

 the recognition of geological horizons, the student could 

 not arrange them correctly except by knowing whence 

 they came. 



4. The science of fossils is called "paleontology," Paieon- 

 literally, the science of that which is old. Paleozoology ^the^* 

 has to do with fossil animals, paleobotany or paleophy- science of 

 tology with fossil plants. The student of these subjects 



is a paleontologist, though we also hear such strange 

 expressions as " fossil botanist." Since fossils are of 

 such fundamental importance for geology, paleontology 

 has long been associated with that science as a division, 

 and is so treated in textbooks. It is, however, obviously 

 part of the study of life, and now that evolution is made 

 the cornerstone of biology, the whole subject acquires 

 new importance. To study the life of today and ignore 

 that of the past is as unprofitable as to study a country 

 or city without taking any account of its history. 



5. Dr. Charles Schuchert of Yale University has The geologic 

 published a "Geologic Time Table" which, though not ' 

 pretending to exactness, represents the most expert 

 consideration of the available evidence. The time rep- 

 resented since the beginning of the Cambrian, where 



we first meet with satisfactory fossils, may have been 



