least ten per cent, of combustible matter. It is known in the Western States as black shale. Its precise geological horizon has been a subject of debate. The conclusion of the author is that "the Huron Shale of Ohio is made up of the black shales of the Lower Portage and Genesee." This deposit is an interesting one, from the fact that it is the most important source of supply of petroleum in this country, and also that most of the gas-wells of Ohio and Pennsylvania derive thence their supply of carburetted hydrogen.
If space permitted, we would be glad to present the views of Professor Newberry on the buried river channels—evidences of glacial action—clay deposits of the Drift age, and other subjects of interest to the geologist.
The reports of the local surveys by counties and districts are not only valuable to geologists, but are throughout of a thoroughly practical character. These include thirty-four counties of the State, besides reports of the Hocking Valley coal-field. Perry, and portions of Athens, and Hocking Counties, and the Hanging Rock District.
The reports of counties are illustrated by maps and charts, of which there are twenty, while fifty-three illustrations are printed with the text.
In the preface we are informed that Vol. IV., Zoölogy and Botany, is now in the printer's hands, and that Vol. V., Economic Geology, is in progress. Besides these, full and elaborate maps are in course of preparation.
The work has been issued in editions of 20,000 copies—to the honor of Ohio, be it said.
Distribution of Heat in the Spectra of Various Sources of Radiation. By William W. Jaynes, Ph. D. Cambridge, Mass.: University Press. Pp. 24.
This pamphlet is the thesis presented to the Faculty of Johns Hopkins University by the author upon applying for the degree of Doctor of Philosophy. It first gives an account of former experiments to determine the distribution of heat in the spectrum; and then details the author's elaborate experiments for the determination of the result. There is one plate of apparatus and three large plates of the curves of thermal intensity in different parts of the spectral region. He thus sums up the inquiry: "In concluding this paper there is a strong temptation to speculate upon the meaning of the results obtained. That the geometrical form of the curve should be so nearly the same at all temperatures, and of the same general form for all substances, is a fact that probably must have an important physical interpretation. Does not the similarity of the curves for different substances show a similarity of movement of the ultimate components of the several substances, and so point to a similarity of ultimate composition of all matter, the slight differences in the grouping of these parts giving rise to the comparatively slight variations from the same form? Certainly this is not proof, but is it not evidence? And is it not probable that the superposition upon the radiations from the ultimate atoms of the radiations from the groupings of these atoms should cause the curve, as a whole, to move slightly to a shorter or longer wave-length, as the weight of a group is lighter or heavier? But I am aware that such speculations are founded on too insufficient data, and I offer these results merely as an experimental contribution to the science of radiant energy."
A Defense of Philosophic Doubt, being an Essay on the Foundations of Belief. By Arthur James Balfour, M. A., M. P. Pp. 355. Price, $3.50.
The object of this book would not be guessed from its title. It would be supposed to imply an argument in favor of skepticism, unbelief, or freethinking, in their customary applications to religious belief. But this is not the author's aim. On the contrary, the work is "a piece of destructive criticism" directed against the foundations of science. According to the author, it is the function of philosophy to give an account of the grounds of all belief and disbelief, and he labors to show that all the assumptions, principles, postulates, and criteria of truth that are usually taken as the basis of scientific knowledge are illusive and indefensible. The independent existence of an external world is denied; Kant, Hamilton, Mill, and Spencer are refuted; and the conclusion is reached that "science is a system of belief which, for anything we can allege to the contrary, is wholly without proof. The inferences by which it
