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374  its scientific accuracy, make it easy for the general reader. It would have been improved in this respect, however, had a glossary been appended. A few examples of want of care in the use of classificatory terms, and occasional indications of careless proof-reading, are blemishes that may be corrected in a second edition.

Report of the Commissioners of Agriculture for 1872.

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Missouri Iron-Ores. By Adolf Schmidt, Ph. D. Jefferson City, Mo.: Regan & Carter. Pp. 16.

Climate of the Glacial Period. By Thos. Belt, F. G. S. Pp. 44.

Habits of Some American Species of Birds. By Thomas G. Gentry. Pp. 16.

Researches in Acoustics. Paper V. By Alfred M. Mayer. Pp. 42.

Drift of Medical Philosophy. By D. A. Gorton, M D. Philadelphia: Lippincott & Co. Pp. 70.

Supplement to the Calculus of Operations. By John Patterson, A. M. Pp. 8.

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Climate of the Glacial Period.—This subject is discussed, in the October number of the Quarterly Journal of Science, by Mr. Thomas Belt. The cold of the glacial epoch, he thinks, was caused neither by elevation of the land in high latitudes, nor by the position of the earth due to the eccentricity of its orbit, as suggested by Lyell, Croll, and others; but rather by great obliquity of the ecliptic. If the axis of our globe be as that of Jupiter, the days and nights would be twelve hours each, and there would be no succession of seasons. The hot climate of the equator would become more temperate toward the poles, and no snow could accumulate at the sea-level, except, perhaps, immediately around the poles.

With beginning of obliquity of the sun's path, seasons of heat and cold would succeed each other, and these would become respectively lengthened and intensified as the obliquity increased. The long winters of intense cold would cause great accumulation of snow, which the summer could not melt. A climate is made more severe by presence of ice and snow, as many of the sun's rays of both heat and light are reflected, and the earth is not warmed by them. Thus, whatever tends to increase the area of snow increases the severity of the climate. The growth of the ice-sheet would cause it to extend toward the equator, and the movement of warm currents might be arrested. The heat of their waters, before expended in melting ice in the polar regions, would now produce great evaporation along the margin of the ice-belts, and the source of rainfall be augmented.

The great obliquity of the sun's path, contended for by Mr. Belt, exists in the planet Venus, where the tropics overlap the polar circle, and a similar state of things here would give us the glaciers as they existed in the ice-age. Moreover, a change in its obliquity back until the sun's path was over the equator, would give the climate which produced tropical plants within the polar circle. The fact of their existence demonstrates the presence there of a mild climate—as enormous unmelting 