4. The lower fresh-water and estuary marls contain _Melania costata,_ Sowerby, _Melanopsis,_ etc. The bottom bed is carbonaceous, and called the “Black band,” in which _ Rissoa Chastelii_ (Fig. 162), before alluded to, is common. This bed contains a mixture of Hempstead shells with those of the underlying Upper Eocene or Bembridge series. The mammalia, among which is _Hyopotamus bovinus,_ differ, so far as they are known, from those of the Bembridge beds. Among the plants, Professor Heer has recognised four species common to the lignite of Bovey Tracey, a Lower Miocene formation presently to be described: namely, _Sequoia Couttsiæ,_ Heer; _Andromeda reticulata,_ Ettings.; _Nelumbium (Nymphœa) doris,_ Heer; and _Carpolithes Websteri,_ Brong.[4] The seed-vessels of _Chara medicaginula,_ Brong, and _C. helicteres_ are characteristic of the Hempstead beds generally. The _Hyopotamus_ belongs to the hog tribe, or the same family as the Anthracotherium, of which seven species, varying in size from the hippopotamus to the wild boar, have been found in Italy and other part of Europe associated with the lignites of the Lower Miocene period. Lignites and Clays of Bovey Tracey, Devonshire.—Surrounded by the granite and other rocks of the Dartmoor hills in Devonshire, is a formation of clay, sand, and lignite, long known to geologists as the Bovey Coal formation, respecting the age of which, until the year 1861, opinions were very unsettled. This deposit is situated at Bovey Tracey, a village distant eleven miles from Exeter in a south-west, and about as far from Torquay in a north-west direction. The strata extend over a plain nine miles long, and they consist of the materials of decomposed and worn-down granite and vegetable matter, and have evidently filled up an ancient hollow or lake-like expansion of the valleys of the Bovey and Teign. The lignite is of bad quality for economical purposes, as there is a great admixture in it of iron pyrites, and it emits a sulphurous odour, but it has been successfully applied to the baking of pottery, for which some of the fine clays are well adapted. Mr. Pengelly has confirmed Sir H. De la Beche’s opinion that much of the upper portion of this old lacustrine formation has been removed by denudation.[5] At the surface is a dense covering of clay and gravel with angular stones probably of the Post-pliocene period, for in the clay are three species of willow and the dwarf birch, _Betula nana,_ indicating a climate colder than that of Devonshire at the present day.