colluvium is sediment that has moved downslope under the influence of gravity, whereas alluvium is transported by rivers. The difference is significant for viticulture given that hillside vineyards—usually characterized by a thin veneer of fragments of the material higher up the same slope, commonly the bedrock that caps the hill—are generally considered superior to those on plains and valley floors, where alluvium dominates. The grand cru vineyards of chablis, for example, are sited mid-slope on the famous marly Kimmeridgian bedrock but a substantial proportion of the colluvium that coats the slopes consists of fragments of the younger Portlandian hilltop limestone (see geology).
