This bedrock was then covered by a thick layers of sedimentary deposits formed from the eroding Appalachian Mountains over hundreds of millions of years.
(This bedrock; was covered; by a thick layers of sedimentary deposits; T:then) (sedimentary deposits; formed; from the eroding Appalachian Mountains over hundreds of millions of years)
This bedrock sedimentary deposits
was covered formed
by a thick layers of sedimentary deposits T:then
from the eroding Appalachian Mountains over hundreds of millions of years