During the last few years, the native iron-making resources of South Wales have received considerable assistance from the re-discovery and working of some very remarkable deposits of hæmatite in the county of Glamorganshire. I propose in the present article to describe two of the most important, perhaps, of those veins of ore, which are found in the districts of Llantrissant and Llanharry, near Cowbridge, and at Newton Nottage, near Bridgend;—the iron-ore in the latter locality being associated with a very large and curious deposit of manganese, chiefly psilomelane. Prefatory to this description, it may not be out of place to give a few remarks on the physical geology of the surrounding country, inasmuch as this district possesses ample materials to engage the attentive and careful examination of the geologist, particularly in relation to the origin of the mineral deposits in question. The exploitation of these hæmatite-mines will have the effect, commercially, of giving a great development and increased prosperity to the iron-manufacture in the district south of Cardiff; while, as a social result, their being worked will probably bring back to a population, at present agricultural, the mining and metallurgical occupations of the ancient fore-dwellers on the soil, and, what is most desirable, give constant occupation to a very large number of the working classes.