Excerpt from Geological Magazine, or Monthly Journal of Geology, 1916, Vol. 3: With Which Is Incorporated, the Geologist, No; 619 to 630; Decade Vi Although some regard a plastic substance as being a highly viscous liquid, technically it is not. A plastic substance is a solid which, if not overloaded, will carry a load put upon it for an indefinite period without yielding. A highly viscous liquid, however, yields slowly, under any load, however small, and yields the more rapidly the greater the load (stress). Thus, if one stone be placed upon a piece of clay or soft plasticene, and another stone be placed upon a piece of hard brittle pitch, after an interval of a few months the one stone will be found resting as it was placed upon the clay or plasticene, whilst the other stone will have sunk more or less deeply into the brittle pitch. The pitch IS a very stiff liquid and the clay 18 a soft solid. Unde1 the conditions of climate now existing 1n this countx y the ground is seldom very deeply frozen, and consequently the soft bedsb of clay or b1ickearth me almost continuously in the plastic condition, and heavy material in or upon them cannot sink. But when the ground is annually deeply frozen and contains much moisture, for a short time after each thaw the thawed clay or brick earth virtually becomes a liquid for a time and allows heavier materials in or resting upon it to Sink some distance. It is clear that if the process Of_the sinking of a layer of gravel and sand into a lighter layer of soft clay went on long enough, the gravel andsand would eventually all collect beneath a layer of clay at the level to which the thaw penetrated each summer; indeed, some sections Show beds of gravelly clay resting upon and covered by loam, clay, or brickearth, oblique streaks of small stones remaining in the upper deposit. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.