They are interesting. I have a vast number of photos of the local geology. Took a photo of those a few times? (sad??)
They are called 'rip up clasts'. If you imagine a layer of peat being scoured over by an erosive current full of sediment which rips up bits of peat (or coal) from below, which end up being incorporated into the overlying bed as the channels infill and settle out then you have it.
So those bits of coal are from a seam below but have been 'ripped up' by later events. They are a geology classic, they occur in various contrasts, mudstone clasts in sandstone are common as well.
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