FROM THE GEOLOGICAL POINT of view it is not so long ago that waves were crashing against the edge of the Taunus mountain range. Deposits of gravel derived from 20 to 30 million year-old tertiary sediments can be found in many places. Finer sediments such as the Cyrena Marl were deposited in the calmer parts of the sea. The Mainz Basin was uplifted at the end of the Tertiary period, cutting off the link to the oceans. The fine brackish sediments from this period are light green, green-grey and blue-green in colour. In many regions, the Cyrena Marls have subsequently been decalcified. Clays and clay marls determine the soil properties in many famous vineyards around Hattenheim (Nussbrunnen, Wisselbrunnen), Erbach (Marcobrunn) and Hochheim (Domdechaney, Hölle).
      Multicoloured mica-rich clays and sands were mixed during deposition. The subsoil consists of the decalcified clay of the Cyrena Marl. The mottling of the soil developed after the sea had receded. The rise and fall of the groundwater level decalcified the marl. The alternating oxidising and reducing conditions caused iron minerals to discolour.
      In many respects, clay soils are extreme. They are heavy soils, wet in spring. They can store large amounts of water, but due to the strong adhesion to the clay particles, only a small fraction is available to plants. The pores of clay soils are very fine, restricting aeration – „ the soil does not breath“. Water drains very slowly. In spring, the soil is waterlogged and aeration is severely restricted. Therefore, these soils are slow to warm. If the plants get „cold feet“ because of waterlogging, their growth is impeded, which in turn leads to an increased susceptibility to diseases. The high clay content and density of this soil impedes root penetration. Roots cannot grow deep enough to obtain the required amount of water and nutrients. The clay soils dry out in late summer,