In the first place, it is mainly unstratified; its lower formation is altogether so. There may be clearly defined strata here and there in it, but they are such as a tempest might make, working in a dust-heap: picking up a patch here and laying it upon another there. But there
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are no continuous layers reaching over any large extent of country.
Sometimes the material has been subsequently worked over by rivers, and been distributed over limited areas in strata, as in and around the beds of streams.
But in the lower, older, and first-laid-down portion of the Drift, called in Scotland "the till," and in other countries "the hard-pan," there is a total absence of stratification.
James Geikie says:
"In describing the till, I remarked that the irregular manner in which the stones were scattered through that deposit imparted to it a confused and tumultuous appearance. The clay does not arrange itself in layers or beds, but is distinctly unstratified."[1]
"The material consisted of earth, gravel, and stones, and also in some places broken trunks or branches of trees. Part of it was deposited in a pell-mell or unstratified condition during the progress of the period, and part either stratified or unstratified in the opening part of the next period when the ice melted."[2]
"The unstratified drift may be described as a heterogeneous mass of clay, with sand and gravel in varying proportions, inclosing the transported fragments of rock, of all dimensions, partially rounded or worn into wedge-shaped forms, and generally with surfaces furrowed or scratched, the whole material looking as if it had been scraped together."[3]
The "till" of Scotland is "spread in broad but somewhat ragged sheets" through the Lowlands, "continuous across wide tracts," while in the Highland and upland districts it is confined principally to the valleys.[4]