CHAP. XIII TJie Past History of Animals 205 



reptiles, beneath these great amphibians, preceded by hosts 

 of armoured fishes, beyond the first traces of which only 

 backboneless animals are found. Yet throughout the 

 chapters of this record, written during different aeons on the 

 earth's surface, persistent forms recur from age to age, 

 many of them, such as some of the lamp-shells or Brachio- 

 pods, living on from near the apparent beginning even until 

 now. But other races, like the Trilobites, have died out, 

 leaving none which we can regard as in any sense their 

 direct descendants. Other sets of animals, like the Ganoid 

 fishes, grow in strength, attain a golden age of prosperous 

 success, and wane away. As the earth grew older nobler 

 forms appeared, and this history from the tombs, like 

 that from the cradles of animals, shows throughout a 

 gradual progress from simple to complex. 



2. Imperfection of the Geological Eecord. — If complete 

 records of past ages were safely buried in great treasure- 

 houses such as Frederic Harrison proposes to make for the 

 enlightenment of posterity, then palosontology would be easy. 

 Then a genealogical tree connecting the Protist and Man 

 would be possible, for we should have under our eyes what 

 is now but a dream — a complete record of the past. 



The record of the rocks is often compared to a library 

 in which shelves have been destroyed and confused, in 

 which most of the sets of volumes are incomplete, and 

 most of the individual books much damaged. When we 

 consider the softness of many animals, the chances against 

 their being entombed, and the history of the earth's crust, 

 our wonder is that the record is so complete as it is, that 

 from " the strange graveyards of the buried past " we can 

 Icam so much about the life that once was. 



We must not suppose the record to be as imperfect as 

 our knowledge of it. Thus many regions of the earth's 

 surface have been very partially studied, many have not 

 been explored at all, many are inaccessible beneath the sea. 



As to the record, the rocks in which fossils are found 

 are sedimentary rocks formed under water, often they have 

 been unmade and remade, burnt and denuded. The 

 chances against preservation are many. 



