That is to say that the peat from which this lignite formed was deposited in swamps 55 to 65 million years ago.
(That; is; to say that the peat from which this lignite formed was deposited in swamps 55 to 65 million years ago) (the peat; formed; lignite)
That the peat
is formed
to say that the peat from which this lignite formed was deposited in swamps 55 to 65 million years ago
lignite