INTRODUCTION. 
Objects much resembling fishes, shells, plants, and other 
remains of living things, have been noticed in rocks from 
time immemorial. They are so abundant and conspicuous 
in some of the countries round the Mediterranean, where the 
Greek and Roman civilisations flourished, that they cannot 
fail to have attracted the attention of the earliest observers. 
Herodotus, for example, referred to sea-shells from the stone 
quarries in the hills of Egypt and the Libyan desert. Other 
contemporary philosophers and writers made similar observa¬ 
tions, and most of them appear to have reached the very 
natural conclusion that these petrified relics were originally 
buried in the bed of the sea, which had hardened and become 
dry land through the retreat of the waters. 
At this early period in the study of natural philosophy, 
however, it was a common belief that animals could originate 
from the mud or slime of lakes and rivers. There was 
therefore another reasonable explanation of their occurrence 
as petrifactions in stone which seemed simpler, because it 
did not involve any startling theories as to great changes in 
the relations of land and sea. If certain animals could be 
generated in mud, it appeared quite probable that they should 
sometimes remain concealed in their native element without 
reaching the surface, and in that case they would become 
hardened into stone itself. As Theophrastus remarked 
concerning petrified fishes, they might have “ either developed 
from fresh spawn left behind in the earth, or gone astray 
from rivers or the sea into cavities of the earth, where they 
had become petrified.” These bodies thus appeared to be 
mere curiosities, and they were treated as such by Aristotle, 
