At Hoxne, near Diss, in Suffolk, a black peaty mass several feet thick, containing fragments of wood of the oak, yew, and fir, was found, overlying the boulder clay.[107] Professor Vogt believes that this peat bed is of the same age as the lignite beds of Switzerland. In the glacial drift of North America, particularly about Lake Champlain and the valley of the St. Lawrence, there is similar evidence of two glacial periods with an intervening non-glacial or warm period.[108] _Glacial and Inter-glacial Periods of the Southern Hemisphere_—(_South Africa_).—Mr. G. W. Stow, in a paper on the “Geology of South Africa,”[109] describes a recent glaciation extending over a large portion of Natal, British Kaffraria, the Kaga and Krome mountains, which he attributes to the action of land-ice. He sums up the phenomena as follows:—“The rounding off of the hills in the interiors of the ancient basins; the numerous dome-shaped (_roches moutonnée_) rocks; the enormous erratic boulders in positions where water could not have carried them; the frequency of unstratified clays—clays with imbedded angular boulders; drift and lofty mounds of boulders; large tracts of country thickly spread over with unstratified clays and superimposed fragments of rock; the Oliphant’s-Hoek clay, and the vast piles of Enon conglomerate.” In addition to these results of ice-action, he records the discovery by himself of distinct ice-scratches or groovings on the surface of the rocks at Reit-Poort in the Tarka, and subsequently[110] the discovery by Mr. G. Gilfillan of a large boulder at Pniel with _striæ_ distinctly marked upon it, and also that the same observer found that almost every boulder in the gravel at “Moonlight Rush” had unmistakable striæ on one or more sides. In South Africa there is evidence not only of a glacial condition during the Pliocene period, but also of a warmer climate than now prevails in that region. “The evidence,” says Mr. Stow, “of the Pliocene shells of the superficial limestone of the Zwartkops heights, and elsewhere, leads us to believe that the climate of South Africa must have been of a far more tropical character than at present. “Take, for instance, the characteristic _Venericardia_ of that limestone. This has migrated along the coast some 29° or 30° and is now found within a few degrees of the equator, near Zanzibar, gradually driven, as I presume it must have been, further and further north by a gradual lowering of the temperature of the more southern parts of this coast since the limestone was deposited.” “During the formation of the shell-banks in the Zwartkops estuary, younger than the Pliocene limestone, the immense number of certain species of shells, which have as yet been found living only in latitudes nearer the equator, point to a somewhat similar though a more modified change of temperature.”