Page:Popular Science Monthly Volume 56.djvu/87

Rh has been found the Dowagiac stone, of about eleven carats' weight, and only very recently a diamond weighing six carats and of exceptionally fine "water" has come to light at Milford, near Cincinnati. This augmentation of the number of localities, and the nearness of all to the "kettle moraines," leaves little room for doubt that the diamonds were conveyed by the ice at the time of its later invasion of the country.

Having, then, arrived at a satisfactory conclusion regarding not only the agent which conveyed the stones, but also respecting the period during which they were transported, it is pertinent to inquire by what paths they were brought to their adopted homes, and whether, if these may be definitely charted, it may not be possible to follow them in a direction the reverse of that taken by the diamonds themselves until we arrive at the point from which each diamond started upon its journey. If we succeed in this we shall learn whether they have a common home, or whether they were formed in regions more or less widely separated. From the great rarity of diamonds in Mature it would seem that the hypothesis of a common home is the more probable, and this view finds confirmation in the fact that certain marks of "consanguinity" have been observed upon the stones already found.

Not only did the ice mantle register its advance in the great ridge of morainic material which we know as the "kettle moraine," but it has engraved upon the ledges of rock over which it has ridden, in a simple language of lines and grooves, the direction of its



movement, after first having planed away the disintegrated portions of the rock to secure a smooth and lasting surface. As the same ledges have been overridden more than once, and at intervals widely separated, they are often found, palimpsestlike, with recent characters superimposed upon earlier, partly effaced, and nearly illegible ones. Many of the scattered leaves of this record have, however, been copied by geologists, and the autobiography of the ice is now read from maps which give the direction of its flow, and allow the motion of the ice as a whole, as well as that