Rock 365 : Day 18 : Bunter Erratic #365photos

Day 18 : Continuing the glacial erratic from the back garden meme from
the last two days, this is the most common of the erratic clasts that
I find, conglomerate pebbles. These pebbles are rounded, unlike the
granite and limestone clasts, but their rounding comes from fluvial
transport in the Triassic rather than the more recent ice transport.
The clast belongs to the Chester Pebble Beds Formation of the Scythian
Sherwood Sandstone Group (better known as the Bunter Pebble Beds) of
the Cheshire Basin. What I find interesting about this clast is the
presence of hydrocarbon residues on the surface. There is no other
clast type in my garden that shows these marks so this implies that
the Chester Pebble Beds from which this was eroded by the ice sheet
contained hydrocarbons.