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."
“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."
“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."
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.
[1. “The Great Ice Age,” p. 21.
2. Dana’s “Text-Book,” p. 220.
3. “American Cyclopædia,” vol. vi, p. 111.
4. “Great Ice Age,” Geikie, p. 6.]
“The lowest member is invariably a tough, stony clay, called ‘till’ or ‘hard-pan.’ Throughout wide districts stony clay alone occurs."
“It is hard to say whether the till consists more of stones or of clay."
This “till,” this first deposit, will be found to be the strangest and most interesting.
In the second place, although the Drift is found on the earth, it is unfossiliferous. That is to say, it contains no traces of pre-existent or contemporaneous life.
This, when we consider it, is an extraordinary fact:
Where on the face of this life-marked earth could such a mass of material be gathered up, and not contain any evidences of life? It is as if one were to say that he had collected the detritus of a great city, and that it showed no marks of man’s life or works.
“I would reiterate,” says Geikie, “that nearly all the Scotch shell-bearing beds belong to the very close of the glacial period; only in one or two places have shells ever been obtained, with certainty, from a bed in the true till of Scotland. They occur here and there in bowlder-clay, and underneath bowlder-clay, in maritime districts; but this clay, as I have shown, is more recent than the till—fact, rests upon its eroded surface.”