Russel Wallace : Alfred Russell Wallace (sic)
"The plains for a distance of from five to twenty miles from the foot of the Sierra Nevada are covered with what are locally termed 'hog-wallows.' The surface thus designated may be represented on a small scale by covering the bottom of a large flat dish with eggs distributed so that their longer axes shall lie at various angles with one another, and then filling the dish with fine sand to a little more than half the height of the eggs. The surface of the sand and of those parts of the eggs which rise above it, gives a fair representation of the 'hog-wallow' land. The mounds, which are represented by the eggs, vary from two to five feet in height, and from ten to thirty feet in diameter, some being nearly circular, some oval, while others are more irregular in shape. Those nearest the foot-hills are the largest, and they gradually diminish in size as they extend out into the plain. They are composed of gravel and boulders of irregular sizes, generally covered with a surface-soil, but sometimes bare. These tracts, which are very extensive in some parts of the State, have been till lately unexplained; but it is now generally admitted that they are due to the retreat of the broad foot of the glacier, leaving behind it a layer of débris or moraine-matter, which has become arranged in its present form by the innumerable rills that issued from the retiring sheet of ice. A living glacier has lately been discovered far up in the Sierra Nevada, near the head waters of the San Joaquim River."
Perhaps some of your geological readers may know if any similar formations occur elsewhere; and may favour us with their views as to whether so extensive and uniform a deposit could be due to a retreating glacier alone, or would not rather require the agency [[p. 275]] of a temporary submergence to spread out the débris with such uniformity. During the retreat of the waters, pluvial action might perhaps wash away the softened soil in the regular manner described.
Alfred R. Wallace