Let us first consider the Carboniferous geography of the northern hemisphere; and in doing so we may begin with a fact concerning the preceding age. One of the most remarkable features of the Newer Devonian is the immense quantity of red rocks, particularly red sandstones, contained in it. Red sandstones, it is true, occur in older formations, but comparatively rarely; their great head-quarters, both in Europe and America, in so far as the Palæozoic is concerned, are in the Upper Devonian. Now red sandstone is an infallible mark of rapid deposition, and therefore of active physical change. If we examine the grains of sand in a red sandstone, we shall find that they are stained or coated, externally, with the peroxide of iron, or iron rust; and that this coating, with perhaps a portion of the same substance in the intervening cement, is the cause of the colour. In finer sandstones and red clays the same condition exists, though less distinctly perceptible. Consequently, if red sands and clays are long abraded or scoured in water, or are subjected to any chemical agent capable of dissolving the iron, they cease to be red, and resume their natural grey or white colour. Now in nature, in addition to mechanical abrasion, there is a chemical cause most potent in bleaching red rocks, namely, the presence of vegetable or animal matter in a state of decay. Without entering into chemical details, we may content ourselves with the fact that organic matter decaying in contact with peroxide of iron tends to take oxygen from it, and then to dissolve it in the state of protoxide, while the oxygen set free aids the decay. Carrying this fact with us, we may next affirm that iron is so plentiful in the crust of the earth that nearly all sands and clays when first produced from the weathering of rocks are stained with it, and that when this weathering takes place in the air, the iron is always in the state of peroxide. More especially does this apply to the greater number of igneous or volcanic rocks, which nearly always weather brown or red. Now premising that the original condition of sediment is that of being reddened with iron, and that it may lose this by abrasion, or by the action of organic matter, it follows that when sand has been produced by decay of rocks in the air, and when it is rapidly washed into the sea and deposited there, red beds will result. For instance, in the Bay of Fundy, whose rapid tides cut away the red rocks of its shores and deposit their materials quickly, red mud and sand constitute the modern deposit. On the other hand, when the red Band and mud are long washed about, their red matter may disappear; and when the deposition is slow and accompanied with the presence of organic matter, the red colour is not only removed, but is replaced by the dark tints due to carbon. Thus, in the Gulf of St. Lawrence, where red rocks similar to those of the Bay of Fundy are being more slowly wasted, and deposited in the presence of sea-weeds