The part of the province of Simbrisk lying to the north of Alatyr, in the angle between the Soura and the Alatyr rivers, is formed of Lower Cretaceous strata, chiefly Neocomian clays, covered by Boulder-clay (which is not rich in boulders), and part by Glacial and Æolian sands. The same Neocomian clay expands widely to the south and to the east from the town of Alatyr. Upon the northern border of the Alatyr valley, and on the right side of the Soura river, these clays are covered by ancient alluvial sands, deposited probably at the time when the great ice-sheet dammed the course of the Soura in the lower part of its valley, and caused colossal overflowings of its waters, the traces of which are preserved in the great masses of alluvial sands covered with fir wood, and much resembling the “Haidesand” of Northern Germany.