They were formed by the deposition millions of years ago of the remains of vegetation (coal) and living organisms (oil and gas), which were buried under subsequent deposition and later subjected to heat and pressure.
(They; were formed; by the deposition millions of years; T:ago) (living organisms; were buried; L:under subsequent deposition) (living organisms; subjected; to heat and pressure; T:later)
They living organisms living organisms
were formed were buried subjected
by the deposition millions of years T:ago
L:under subsequent deposition
to heat and pressure T:later