CHAP, xvin PAST HISTORY 347 



first traces of which only backboneless animals arc found. 

 Yet throughout the chapters of this record, written 

 during different aeons on the earth's surface, persistent 

 forms recur from age to age, a few of them, such as some 

 of the lamp-shells cr Brachiopods, 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. 



O */ 



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 ap- 

 peared, and this history from the tombs, like that from 

 the cradles of animals, shows throughout a gradual 

 increase of differentiation and integration. It must 

 always be borne in mind, however, that a type which is 

 on the whole of low degree may show extraordinary 

 complexity and harmony in detail. 



2. Imperfection of the Geological Record. If complete 

 records of past ages were safely buried in treasure-houses 

 such as some historians have proposed to make for the 

 enlightenment of posterity, then palaeontology would be 

 easv. Then a ^enealoo-ical tree connecting the Protist 



/ o c* c* 



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 learn 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 



