GEOLOGY. The surface geological formations of the northern plain are mainly Quaternary sands and clays of alluvial glacial deposit, with an occasional patch of firm Tertiary formation emerging from it. The great central highland is represented by all the formations, but is chiefly Mesozoic. On the southern border of the Quater nary plain where the highlands begin, there are in the region of the Weser highland narrow transition bands of the Cretaceous and Jura for mations, which are replaced a little farther south by the great central area of Triassic rocks. On the west of the Weser highland the Quaternary formation of the north is replaced on the south by a broader Cretaceous zone, somewhat inter rupted by the Quaternary, and south of the Lippe in the region of the Ruhr is a narrow belt of Dyassic and coal formation which in the Sauerland highlands is replaced by the extensive Devonian and Silurian areas of the middle Rhine, and which extends far to the westward into France. These formations are interrupted by patches of eruptive rocks and Tertiary forma tions, and are bordered on the south directly on the Rhine by Tertiary formations, which, how ever, are soon replaced by the Quaternary, which characterizes the upper middle Rhine Valley, and which interrupts the great Triassic area of Cen tral and Southern Germany. West of the Rhine the Quaternary formations of the northern plain extend much farther south than east of the Rhine, and with progress southward are replaced, after slight interruptions, by Tertiary and Triassic for mations, by the extensive Devonian and Silurian areas, which are separated from the extensive Triassic area of the south by the Dyassic and coal formations in the Oldenburg region. In the
region of the Black Forest on the east and of the Vosges Mountains on the west of the Rhine Valley are extensive areas of old crystalline rocks. In the Harz Mountains the central area of Devonian and Silurian formations is sur rounded by a narrow strip of Dyassic formation which on the south is replaced by the Triassic, until interrupted by the Thuringian Forest by re curring Dyassic, Devonian, and Silurian forma tions. The great central Triassic area is bordered en the south by the long Jurassic chain consisting of the Swiss, Swabian, and Franconian Juras, which extend on the north side of the Rhone, the Aar, and the Danube from the Rhone to the Main. Parallel to this chain and south of the Aar and the Danube is the extended Tertiary area of the Alpine Foreland and the Chalk Alps, which is separated from the central Alpine region of old crystalline rocks by a narrow border of Jurassic formation. Germany has been glacier covered as far south as latitude in the western and in the eastern part.