Second, they are hundreds to thousands of times larger in area than their bedrock sources. Third, they have sharp lateral and vertical contacts with the enclosing till. Fourth, they climb gently within the enclosing till, down-ice from their sources, meaning the head of the train may be buried but the tail may reach the surface. The broad tail of a train is usually detected first. Discovery Dispersal trains are usually found by prospecting and geochemical or mineralogical studies of till.
Prospectors look for ore boulders protruding from the till.
Till samples, collected at the surface or from drillholes on a regular grid covering the favorable bedrock, are analyzed chemically or mineralogically to measure metal or mineral content. Glacial dispersal trains can be hundreds of kilometres long. Trains of this size are detected only when the area sampled is very large and when the train's characteristic lithological component is present in adequate amounts to make it distinctive against background rock types in the dispersal area. Large trains can best be detected by 'reconnaissance' scale till sampling at a density of one sample per 100 km 2 . Smaller dispersal trains derived from individual rock units and distinctive belts of rock are more likely to be detected early in mineral exploration programs.