And the “ Great Carolina Marl Bed.” 35 
taken by the silica; for in no other way can we 
account for the preservation of the most minute strize 
on the shells together with every spine, process or 
other characteristic mark.” 
In confirmation of the above, Professor Tuomey 
found in Orangeburg District a fossil containing fad 
silica. He says: “At first it resembled thin trans- 
parent jelly, but on exposure to the air it changed 
color, becoming milky, and, finally, became hard, and 
presented the appearance of Pearl-stone.’ Thus we 
can readily understand how a shell composed mostly 
of lime, will, under certain conditions, become flint, 
retaining its form and prominent characteristics. 
WHAT ARE FOSSILS AND PETRIFACTIONS. 
[From the Boston Journal of Chemistry. ] 
“Every one who has read even an elementary 
manual of geology knows that the remains of plants 
and animals are found in the crust of the earth more 
or less petrified, or converted into stony matter. 
They are commonly known as /osse/s, a term which 
etymologically means nothing more than dug up. To 
the men of old time and even to the earlier geologists, 
their occurrence was a riddle and few considered 
them as other than mere accidents or lusus nature ; 
but to the geologist of our day they are pictures in 
the great stone-book of the earth’s history, illustrating 
the life that peopled the lands and waters in pre- 
