Wartime Lessons in Erosion

Extract

During September, 1940, there were many falls of earth and other things upon the roofs of London. An example that I had excellent opportunities of studying consisted of loam, and gravelly loam, distributed in discrete patches over an extensive area. The material must have fallen from a considerable height, for everywhere it moulded itself with flat base to suit its foundation; and, whether forming mere pellets or splashes a few feet in diameter, it developed a surprisingly uniform summit level of little more than 1 inch in height. On breaking the loam across, one always found a system of close, roughly horizontal cracks, a type of rude joint cleavage. This structure persisted despite frequent wettings and dryings, even though when wet the loam became quite sodden.