Coal and petroleum / crude oil
are very important non-renewable energy resources that might one day run out.
ONTA is a geology company that makes different kinds
of educational coal and petroleum / crude oil sample sets.
They show how coal and oil are made in and come from the earth and how
they are similar to and different from each other.
These sets can all be seen by pressing on any of the different numbered page links located on
the left hand side column.