crust breaks away from the surface of _Orbulina_, leaving a thin inner sphere, at first beautifully transparent, but soon becoming opaque and crumbling away. "In the meantime the proportion of the amorphous 'red clay' to the calcareous elements of all kinds increases, until the latter disappear, with the exception of a few scattered shells of the larger _Foraminifera_, which are still found even in the most characteristic samples of the 'red clay.' "There seems to be no room left for doubt that the red clay is essentially the insoluble residue, the _ash_, as it were, of the calcareous organisms which form the _Globigerina_ ooze, after the calcareous matter has been by some means removed. An ordinary mixture of calcareous _Foraminifera_ with the shells of pteropods, forming a fair sample of _Globigerina_ ooze from near St. Thomas, was carefully washed, and subjected by Mr. Buchanan to the action of weak acid; and he found that there remained after the carbonate of lime had been removed, about 1 per cent. of a reddish mud, consisting of silica, alumina, and the red oxide of iron. This experiment has been frequently repeated with different samples of _Globigerina_ ooze, and always with the result that a small proportion of a red sediment remains, which possesses all the characters of the red clay." * * * * * "It seems evident from the observations here recorded, that _clay_, which we have hitherto looked upon as essentially the product of the disintegration of older rocks, may be, under certain circumstances, an organic formation like chalk; that, as a matter of fact, an area on the surface of the globe, which we have shown to be of vast extent, although we are still far from having ascertained its limits, is being covered by such a deposit at the present day. "It is impossible to avoid associating such a formation with the fine, smooth, homogeneous clays and schists, poor in fossils, but showing worm- tubes and tracks, and bunches of doubtful branching things, such as Oldhamia, silicious sponges, and thin-shelled peculiar shrimps. Such formations, more or less metamorphosed, are very familiar, especially to the student of palaeozoic geology, and they often attain a vast thickness. One is inclined, from the great resemblance between them in composition and in the general character of the included fauna, to suspect that these may be organic formations, like the modern red clay of the Atlantic and Southern Sea, accumulations of the insoluble ashes of shelled creatures. "The dredging in the red clay on the 13th of March was usually rich. The bag contained examples, those with calcareous shells rather stunted, of most of the characteristic deep-water groups of the Southern Sea, including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha, Pourtalesia_, and one or two _Mollusca_. This is, however, very rarely the case. Generally the red clay is barren, or contains only a very small number of forms."