During the re-excavation of the basin of the Rhine successive deposits of loess of newer origin were formed at various heights; and it is often difficult to distinguish their relative ages, especially as fossils are often entirely wanting, and the mineral composition of the formation is so uniform. The loess in Belgium is variable in thickness, usually ranging from 10 to 30 feet. It caps some of the highest hills or table-land around Brussels at the height of 300 feet above the sea. In such places it usually rests on gravel and rarely contains shells, but when they occur they are of Recent species. I found the Succinea oblonga, before mentioned, and Helix hispida in the Belgian loess at Neerepen, between Tongres and Hasselt, where M. Bosquet had previously obtained remains of an elephant referred to E. primigenius. This pachyderm and Rhinoceros tichorhinus are cited as characterising the loess in various parts of the valley of the Rhine. Several perfect skeletons of the marmot have been disinterred from the loess of Aix-la-Chapelle. But much remains to be done in determining the species of mammalia of this formation and the relative altitudes above the valley-plain at which they occur. If we ascend the basin of the Neckar, we find that it is filled with loess of great thickness, far above its junction with the Rhine. At Canstadt near Stuttgart, loess resembling that of the Rhine contains many fossil bones, especially those of Elephas primigenius, together with some of Rhinoceros tichorhinus, the species having been lately determined by Dr. Falconer. At this place the loess is covered by a thick bed of travertine, used as a building stone, the product of a mineral spring. In the travertine are many fossil plants, all Recent except two, an oak and poplar, the leaves of which Professor Heer has not been able to identify with any known species.