While the number of the diamonds sown in the drift is undoubtedly large, their dispersion is such that it is little likely they can be profitably recovered. The distribution of the localities at which stones have thus far been found is set forth upon [Fig. 334]. Obviously those that have been found are the ones of larger size, since these only attract attention. In 1893, when the finding of the Oregon stone drew attention to these denizens of the drift, the writer prophesied that other stones would occasionally be discovered under essentially the same conditions, and such discoveries are certain to continue in the future.
Fig. 334.—Glacial map of a portion of the Great Lakes region, showing the unglaciated area and the areas of older and newer drift. The driftless area, the moraines of the later ice invasion, and the distribution of diamond localities upon the latter are also shown. With the aid of the directions of striæ some attempt has been made to indicate the probable tracks of more important diamonds, which tracks converge in the direction of the Labrador peninsula.
Tabulated comparison of the glaciated and nonglaciated regions.—It will now be profitable to sum up in parallel columns the contrasted peculiarities of the glaciated and the unglaciated regions.
| Unglaciated Region | Glaciated Region |
| TOPOGRAPHY | |
| The topography is destructional;the remnants of a plain are foundat the highest levels or upon thehill tops; hills are carvedof a high plain; unstable erosionremnants are characteristic. | The topography is constructional;the remnants of a plain are foundat the lowest levels in lakes andswamps; hills are molded above aplain in characteristic forms; nounstable erosion remnants, but onlyrounded shoulders of rock. |
| DRAINAGE | |
| The area is completely drained,and the drainage network isarborescent. | The area includes undrainedareas,—lakes and swamps,—andthe drainage system is haphazard. |
| ROCK MANTLE | |
| The exposed rock is decomposedand disintegrated to aconsiderable depth; it is all oflocal derivation and hence of fewtypes—homogeneous; the fragmentsare angular; soils are leached andhence do not contain carbonates. | No decomposed or disintegratedrock is “in place”, but onlyhard, fresh surface; loose rockmaterial is all foreign and of manyizes and types—heterogeneous;rock bowlders and pebbles arefaceted and polished as well asstriated, usually in severaldirections upon each facet; soilsare rock flour—the grist of theglacial mill. |
| ROCK SURFACE | |
| Rock surface is rough andirregular. | Rock surface is planed or grooved,and polished. Shows glacial striæ. |
Unassorted and assorted drift.—The drift is of two distinct types; namely, that deposited directly by the glacier, which is without stratification, or unassorted; and that deposited by water flowing either beneath or from the ice, and this like most fluid deposited material is assorted or stratified. The unassorted material is described as till, or sometimes as “bowlder clay”; the assorted is sand or gravel, sometimes with small included bowlders, and is described as kame gravel. To recall the parts which both the glacier and the streams have played in its deposition, all water-deposited materials in connection with glaciers are called fluvio-glacial.
Fig. 335.—Section in coarse till. Note the range in size of the materials, the lack of stratification, and the “soled” form of the bowlders.