Devon is not so much known for its coal production as it is for its tin, lead or copper; but produced it was in its less-useful ores. Anthracite or Hard Coal has been mined in a number of locations around the district of Bideford; namely for use in black dyes. Lignite, or "Brown coal" is characterised by its low quality, leaving its only viable use as for the fireplace.
That this was known as early as 1775 is shown through the writings of Josiah Wedgwood (yep, the guy who made your fine china) through the survival of his diary. This was written whilst out prospecting for sources of his new "china clay" in the southwest:
"The coals if one may call them so, at Bovey Tracey, are of a very singular species. They bear but little resemblance to the pit coal of Staffordshire and other places, nor do they lie in continued regular seams. They seem to be something between wood and coal, partaking as much of the nature of the former as of the latter. They seem like fossil wood, flatted by the incumbent earth, and on some pieces I took up myself I thought I could distinguish the knots which are on the outside of trees. They lie in an imperfect rough white clay, interspersed with small shivers of the coal between the larger layers of it. Some of these layers are from 4 or 6 inches to 4 or 6 feet in thickness
They are got by open work. The open pit I saw was about 40 feet deep, in which were at least 20 of these layers, one over another, and the layers are thicker and better the deeper they lie in the ground."
And went on to note:
"The Coals are only 2/6 per ton, at the pit, and so near to the [pottery] works, that only wheelbarrows are used for their conveyance to the works."
The pottery works in question were those of his rival: a Mr Crisp and Sanders, whom had preceded Wedgwood's future work by a decade and a half. It appears that the coal mine had been first opened to coincide with the factory here, as no earlier reference is known of at this stage.
Wedgwood eventually went on to far exceed his competition in cultural impact: after all, your gran probably has a bust of baby blue with white detail sitting next to her Peter André CD on the mantelpiece.
Brown coal was again recorded as being worked here in absence of the pottery under the "Devon Lignite Works" in 1893. Three seams were being worked; the Somersetshire code code without safety lamps were introduced in 1891.
Data courtesy of Ben Sum, Helston (14/12/18).
NB: CRO = Cornwall Records Office, Truro (Soon to be Kressen Kernow, Redruth)
DRO = Devon Heritage Centre, Exeter
[CRO] Diary of Journey to Cornwall, Josiah Wedgwood 1775
[DRO] Brooke Index for Devon
Ordnance Survey County Series