Page:Popular Science Monthly Volume 50.djvu/403

Rh water, as our lake ore is, it of course has great freedom of movement, and we therefore find it in flat concretions, more or less porous and circular in outline; the general appearance amply justifying the term "cake ore," which is locally applied. These concretions vary much in size, some of them being no larger than mustard seeds, others eight or ten or more inches in diameter. Frequently the larger cakes are joined together and form masses looking not unlike batches of a certain kind of bun commonly exposed in the shop window of every confectioner, and made by coiling a strip of dough round and round a piece of itself.

The ore is not found over the whole lake bottom; it occurs along the whole margin, and also well out from shore where streams enter the lake, the distance of the ore deposit from shore depending, of course, upon the volume of water carried by the streams and the velocity with which it enters the lake. Certain strips of ore occur at a considerable distance from the shore and in as much as sixteen feet of water. These deep-water, mid-lake deposits denote probably the courses of former streams which are now nonexistent, owing to some change of level.

Not only is this lake an iron mine, it is more; it is something like the widow's cruse of oil of which we read in Holy Writ—the supply is being constantly renewed. Vast amounts of iron still exist in the surrounding sands. Vegetable acids are formed from the decay of each year's vegetation, and each year the drainage carries into the lake and deposits there a large amount of iron. This is no mere theory: one can actually see the deposition of the ore along the margin, and, moreover, it is found in actual working; if a certain spot be worked out, it will in a few years again yield ore in paying quantity.

Lake ores are abundant in northern Europe, but, so far as the writer's knowledge extends, Lac à la Tortue and a neighboring lake are the only instances of the kind in North America. The ore is extracted from our lake mine by hand and by power. The shallow margin is divided into sections and allotted to suitable parties who may desire to work them and who are paid at a specified rate per ton of ore raised. Two men generally work in company. Their implements are a shovel, a strong circular sieve, and a rough hand barrow. When work is to be begun the workmen remove shoes and stockings and use their feet in searching for ore which lies imbedded in the soft sand, nothing coarser than sand, except ore cakes, being found in the lake. Guided by their feet, the workmen put down their shovels and bring to the surface a quantity of ore and sand which they throw into their circular sieve. This is then held below the surface of the water