As this chapter necessarily touches less on popular and more on scientific matters than the rest of this book, a few more words may be added on the palæontology and geology of Madagascar. Besides those extinct creatures already spoken of, remains of gigantic tortoises have been discovered; also species of swine and river-hog; an ox differing from the existing cattle of the country, and a large rail and a goose exceeding in size any living species. All these belonged to the Quaternary and Recent geological epochs. But far back in the period of the Secondary rocks a species of sloth lived in the forests, old forms of crocodile lived in the rivers; and there were three at least of those gigantic lizards which were the largest of all known land animals, and were the master existences of the Jurassic period. To sum up in a sentence or two the salient features of Madagascar geology, it may be said that the whole eastern part of the island from north to south, comprising probably about three-fifths of the entire area, is composed of crystalline rocks—gneiss, granite, mica-schist, etc. But the western two-fifths of its surface consists chiefly of Secondary strata, including chalk and sandstones and limestones of the Jurassic and Cretaceous, periods, as well as a smaller area of rocks of the Eocene and Oligocene eras. A fringe of Quaternary deposits is also found along a great part of the west coast. It is evident, therefore, that the western side of the island has been repeatedly under the sea during the geological periods just mentioned, leaving the upper highland of ancient rocks as an island not half the extent of the present Madagascar. It has quite recently been found that a narrow edging of chalk rock extends for about one hundred and twenty miles on the central part of the east coast.[24] Plutonic rocks are found in several places in both the great geological divisions of the island, and also many outflows of volcanic rocks, of a much more recent date.