<P> The river valley's geological formation is mainly of crystalline rocks, interspersed with Tertiary and Quaternary deposits in the wider reaches of the valley, and also in the Spitzer Graben . The land formation in the valley is dictated by the clay and silt deposits around Weissenkirchen and at the beginning of the Wachau stretch . A major tributary, which joins the Danube in Wachau on its left bank, is the Spitzer Graben, which is stated to be "part of the primeval Danube ." During the Tertiary period, the flow of this river was to the west of the Wachau, on its northern border . The course of the river seen now is from Spitz onwards . The river is flowing along a weak fault zone on the southern border of the Bohemian Massif . </P> <P> The origin of the wine growing tradition in Austria, and in particular in the Wachau valley, and its popularity beyond its borders, is attributed to medieval period of the Roman settlements . The Vinea Wachau Nobilis Districts date to Leuthold I von Kuenring (1243--1313). Wine production peaked under the Carolingians . Krems has a long history as the hub of the Wachau wine trade, while the town of Dürnstein is also known for being one of the Wachau wine centres . Founded in 1983, the Vinea Wachau is an association of vintners who created categories for Wachau wine classification . The vintners of the Vinea Wachau claim to produce quality wine under a manifesto of six Vinea Wachau wine making laws, also known as six Wachau commandments . Their products, known for their purity, are labelled under the categories of Steinfeder, Federspiel or Smaragd . </P> <P> The Wachau valley is well known for its production of apricots and grapes, both of which are used to produce specialty liquors and wines . The wine district's rolling vineyards produce complex white wines . Wachau is a source of Austria's most prized dry Rieslings and Grüner Veltliners, some of the best from the steep stony slopes next to the Danube on which the vines are planted . The temperature variation in the valley between day and cold nights has a significant role to play in the process of ripening of the grapes . The heat retained in the water and the stoney slopes with thin soil cover facilitates this process of growing fine variety of grapes, which results in the sophisticated wines produced in the valley . Since rainfall is not adequate for the growth of wines on thin soils, irrigation is an essential requirement to give water supply to the wine yards . </P> <P> The historical monuments in the Wachau valley are more than 5000 . Some of them are: The Benedictine abbeys of Melk (Stift Melk a massive baroque Benedictine monastery) and Göttweig (a monastery of canons regular), at the beginning and end of the scenic Wachau section of the Danube Valley from where one gets a visual feast of the city of Melk; the Schallaburg Castle, a Renaissance style castle 4 kilometres (2.5 mi) from Melk; the Steiner Tor in Krems or Krems an der Donau, the late - Gothic Piarist church; Dürnstein for its wine growing area and the Durnstein castle; and the Burgruine Aggstein . </P>

The wachau valley is noted for its production of what product