The essential peculiarity of the veins at Thetford is that they are occasionally associated, as already mentioned, with grains and threads of chromic iron and also of magnetite. The magnetite forms rather conspicuous masses between the veins of asbestos in Messrs. King's mine, where it sometimes entirely replaces the latter.[8] As a general rule, however, the surface veins at Thetford are nearly as pure as those lying deeper in the rock, the reason being that the surface is mostly naked rock only scantily clothed with vegetable mould, moss, or other foreign element, contact with which deteriorates, by discolouring, the fibre, as is found to be the case in a very marked degree in the mines next to be described. It is a peculiarity of the veins of asbestos that they are never continuous. They vary very much in size, and, in precisely the same way as other mineral veins, they are affected by faults or slides, which not infrequently cut off completely a valuable working face. Where this occurs the slicken-sided character is very marked. Sheets, also, of imperfect or immature asbestos, having a long coarse woody fibre, are frequently to be seen lying all along the sides of the fault; but, although there is a good deal of this, the general quality of the produce of all the Thetford mines is excellent. The fibre is fine and of a smooth silky texture, very easily worked. The veins are mostly, especially in the lower cuttings, more free from impurities than those of Coleraine. No steam power is at present used in this district, the whole of the proprietors at present continuing to rely upon hand labour; the Boston Company are, however, as just mentioned, now seriously turning their attention that way, with a view of increasing their output. The Thetford mine-owners are one and all kind and hospitable men, always ready to give every information and to facilitate an inspection of their works by anyone who will take the trouble to visit them; a trouble which I always found very amply repaid by the courtesy with which I was received, and the candour and obliging readiness with which all my inquiries were immediately answered. The workers in the mines here are mostly resident on the spot, sufficient accommodation having been provided for them in the immediate neighbourhood of the mines; the proprietors, who appear to act with a liberal consideration towards their men, deeming it incumbent on themselves to look after their welfare; and they find their account in so doing, in not running short of hands at critical times.