Page:Popular Science Monthly Volume 10.djvu/651

Rh says the author, "is with some limitations an expression of force."

Cephalization is shown both in embryonic development and in the progress of life in geological history. The law is further illustrated by the discoveries of Prof. Marsh, from which it appears that the brains of the great mammals of the early Tertiary were very much smaller than those of allied species of recent time. Thus the brain of the dinoceras, of the Eocene, was not more than one-eighth the size of that of the modern rhinoceros, showing an immense development of the brain, while the bulk of the animals has decreased. We have also a development of those features of both form and capacity which are characteristic of brain-power.

The increase of the brain and nervous system may arise, the author suggests, from the fact that this part of the structure comes in contact with outside and inside Nature, and is the means by which the animal has communication with the outer and inner world, and with its own inner workings and appetites. This constant and energetic use of the brain may have given to it its wonderful growth and strength since Eocene times.

But brain-progress could not have taken place without structural progress, and structural changes have been determined by it. Brain-force reacts upon and modifies both form and structure.

It is not claimed by the author that the theory of cephalization accounts for all the types of structure found in the animal world, but only that whatever these types may have been in course of development they were in general subordination to the principle of cephalization. "The origin of the grander types of structure," writes Prof. Dana, "must be connected with the profoundest of molecular laws; and how connected man may never know. These views may hold, whatever be the true method of evolution. The method by repeated creations should be subordinated, as much as any other, to molecular law and all laws of growth; for molecular law is the profoundest expression of the Divine will. But the present state of science favors the view of progress through the derivation of species from species, with few occasions for Divine intervention. If, then, there has been derivation of species from species, we may believe that all actual struggles and rivalries among animals leading to 'survival of the fittest' must tend, as in man, to progress in cephalization and dependent structural changes."

On the Origin of Prairies.—Having shown, in an article which we noticed in the December number of the the untenableness of the current hypotheses with regard to the origin of prairies, Prof. J. D. Whitney now presents, in the American Naturalist, a theory of his own. He finds, as the result of a great number of observations made over all the prairie States, that almost without exception absence of forests is connected with extreme fineness of soil, and that this fine material usually occurs in heavy deposits. "No person," he remarks, "can have traveled through Southern Wisconsin, Illinois, Iowa, or Missouri, without having had everywhere occasion to observe that the prairie-soil is exceedingly fine and deep; there are whole counties in Iowa in which not a single pebble can be found." The distribution of the timbered and prairie tracts in Wisconsin affords a good test of the correctness of the author's hypothesis. In the northern part of the State is a region of dense forest, though this is not a region of large precipitation. It is, however, heavily covered with coarse detrital materials, plentifully distributed from the headquarters of the drift on Lake Superior. The rocks underlying the drift-deposits are crystalline, belonging to the Azoic series, and the surface is rough and broken, being intersected with low ridges and knobs of granite and trap. South of this is a large area, occupying the central portion of the State, and extending as far as the Wisconsin River, almost exclusively occupied by a very pure siliceous sandstone, which is wrapped about the Azoic region, extending in a northeasterly direction to the Menomonee River, and northwest to the falls of the St. Croix. This great sandstone-covered area is the pine-district of the State, while south of the Wisconsin is the region of oak-openings and prairies. When we reach these treeless tracts we have got entirely beyond the drift-covered area, and are upon a soil made up of the insoluble residuum left from