Arn Gill is a ravine or gully containing a beck of the same name, near the village of Muker in Swaledale, North Yorkshire, England.

The beck runs east–west in its gully, falling steeply downhill from its source on the fell Arn Gill Head, to its discharge point as a tributary of the River Swale.

But when the deeper Adelaide Level was driven there, in 1865, a rich vein of ore was found by Sir George Denys' A.D. Company.

[14]The deep valleys ramifying through the hills offer frequent opportunities for driving adit levels at various elevations, by which mode of access all subsequent operations are carried on at a comparatively small expense.

An adit level judiciously placed facilitates the drainage and ventilation of the mine; it also affords an easy access for the miners, and egress for the ore by means of wagons running on a tramroad, and propelled either by men or horses, thus saving the labour and expense of raising the products by either steam or water power.

In addition to these advantages, the ore is delivered on the banks of a stream, the most convenient place for preparing it for the smelting-house; and should water be required for driving the crushing mills or other machinery, it can ordinarily be obtained from the higher course of the stream; consequently steam power is seldom required and rarely used in this district.

He was struck with the most robust appearance of the miners, and the larger proportion of middle-aged and old men among them ... [Dr Peacock indicated a problem with ventilation and "choke damp".]

In these northern districts, the rates of mortality are much higher among the mining than among the non-mining section of the male population.

The men are not infrequently small farmers, with gardens attached to their cottages, and ground for the keep of a cow, which enables them to take milk, which they take underground ...