392 ELEMENTARY GEOLOGY 
ages since the first; but these are merely fragments 
that have chanced to escape destruction. 
To construct a record from this fragmentary portion 
of the sedimentary series, is difficult and in some eases 
impossible. EKven had the original record been com- 
plete, there would be many gaps where rocks have been 
removed ; but starting with an already fragmentary 
series, this added cause for imperfection makes indeed 
a ragged page. It is like a blurred and faded manu- 
script, which, moreover, comes down to us all tattered 
and torn. 
More than this, even of the organisms that have been 
preserved, only a portion are as yet discovered. Rocks 
deep in the earth have never been examined. Even 
in well-studied regions, it is usually only the very sur- 
face that can be explored. Most of the fossils are 
buried beneath the soil or layers of other rocks; and 
only here and there, in a ledge, or a cliff, or a shaft 
that has been sunk in the earth, can we search for the 
entombed remains of those organisms that have passed 
away. So as exploration proceeds, our knowledge 
of the earth’s past is continually increased, and each 
year brings new and important discoveries. 
In spite of these difficulties and imperfections, enough 
has been learned from the study of fossils to tell the 
outline story of the earth’s development; but only 
enough to make us see the incompleteness of this 
