all the Catskills, measuring 4,205 feet, and is the hydrographic center of the region, whence the waters run to the northwest by the Esopus, to the northeast by Woodland Creek, to the south by the Rondout to the Hudson, and to the southwest by the Nevisink to the Delaware. The geological structure of the group is similar to that of the northern Catskills. Professor James Hall has announced that, after four years of observation, he has detected the existence of four lines of anticlinals, nearly parallel to each other, and running from southwest to northeast, in conformity with the ordinary trend of the Appalachian range. Professor Guyot is willing to acknowledge the fact, but calls attention to the other fact that these axes cross the chains and valleys almost at right angles, "and were probably posterior to the scooping out of the valleys and mountain-chains, on the conformation of which they had so little effect. . . . A hypsometric feature, which may refer to this order of facts, is that the three maxima of altitudes above four thousand feet, the Slide Mountain, Hunter Mountain, and Black Dome, are situated in a straight line, trending from southwest to northeast."
Silicified Forests of the Yellowstone Park.—In Bulletin No. 1 of Vol. V. of the "Geological and Geographical Survey of the Territories," Mr. W. H. Holmes gives an account of a most wonderful geological formation, which attains its greatest development in the valley of the east fork of the Yellowstone River. It occurs in horizontal layers, having an aggregate thickness of fifty-five hundred feet, that is, the whole formation at this point is a little more than a mile in depth. This is filled throughout with the silicified remains of a multitude of forests, many of the trunks of trees that are still to be seen being of very large size. Some of them are prostrate, and from fifty to sixty feet long; others are upright where they grew, and some of the stumps measure from five to six feet in diameter. One gigantic trunk is described that stands twelve feet above the eroded strata about it, and is ten feet in diameter. This trunk is hollow, but the woody structure of what remains is well preserved, the rings of growth being clearly defined. The bark on this stump is four inches thick, and on its outer surface deeply lined. Scattered through the formations among the trunks is a great variety of vegetable remains, consisting of branches, rootlets, fruit, and leaves. Specimens submitted to Professor Leo Lesquereaux have been identified as follows: Aralia Whitneyi, Magnolia lanceolata, Laurus Canariensis, also new species of Fraxinus, Cornus Alnus, Tilia, Diospyros, Pteris, and Fern. The wood is in many cases completely agatized, and cavities which existed in the decayed trunks are filled with crystals of calcite and quartz. The formations are of the "Volcanic Tertiary," and composed of fragmentary volcanic products, breccias, conglomerates, and sandstones, the two former consisting chiefly of basalt. Many are of great size, and are cemented together in enormous masses or heavy beds by tufaceous and other fine grained material. These beds or layers represent successive formations, arising from the subsidence of the land, during the intermissions of which the forests grew. The beds have evidently been changed by the action of water; and the conclusion is that the formation represents the shore or margin of a great Tertiary lake. It is believed that the beds cover or have covered an area of over ten thousand square miles.
Germs of Disease in Water.—Professor Huxley, in a recent discussion of a paper by Dr. Tidy on water for dietetic purposes, said that diseases caused by what people not wisely call germs are produced invariably by bodies of the nature of bacteria. These bodies could be cultivated through twenty or thirty generations, and then, when given under the requisite conditions, would invariably cause their characteristic disease. Bacteria are plants, and we know under what conditions they can live and what they will do. They can be sown and will thrive in Pasteur's solution, just as cress or mustard in the soil; and, if a drop of this solution were placed in a gallon of water, Professor Roscoe thinks it doubtful if there is any known method by which its constituents could be estimated. Every cubic inch of such water would contain fifty thousand to one hundred thousand bacteria, and one drop of it would be capable of exciting a putrefactive fermentation in any substance
