Page:Popular Science Monthly Volume 12.djvu/266

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THE POPULAR SCIENCE MONTHLY.

are informed, "results from combined action of configuration, character of soil, constitution of underlying rock, and the form of its surface. These four elements regulate natural drainage. Each must present favorable conditions, or deadly waters will accumulate on the surface or in hidden strata. No plan of artificial drainage can be completely successful unless based on a thorough comprehension of the natural drainage system of the area under treatment. The region above the Palisades on the Hudson furnishes excellent illustration of these statements. The plateau fronts the river eastward with a bluff 300 feet high, and westward slopes gently to the Hackensack Valley. . . . All topographical conditions of unusual health seem here present, and yet malarial diseases abound. The reason of this will probably be found in the configuration of the rock. The dense basalt underlying the thin soil absorbs almost no water. Its surface, originally nearly level, was worn by glacial action into low, swelling ridges and shallow rock-basins, many of which, having no outlet, hold stagnant water as great saucers would. If the rock were either fissured or porous the height of the plateau would insure perfect under-drainage."

With the Palisades plateau the author now contrasts the Helderberg plateau, also situated near the Hudson River. Here, "an escarpment 1,000 feet high bounds, on the eastern side, the table-land, composed of horizontal limestone resting on shales. From the more level parts water does not pass off by surface-streams. Low undulations divide these areas into many separate basins, each draining toward its own centre, where a funnel-shaped opening in the limestone receives the disappearing flow, whose future course is subterranean. These basins are from a few acres to 300 or 400 in extent. When one covers about five square miles a pond is formed at the point of central drainage, Ending outlet through fissures of the limestone below. The plateau's elevation insures that these waters sink at once many hundred feet, or escape in springs along the cliffs." Mr. Gardner then proceeds to show how—as at Sandusky, Ohio—this same Helderberg limestone may, under different topographical conditions, become one of the most powerful producers of disease.

 

A Formidable Arachnidan.—Dr. B. F. Pope, U. S. A., contributes to Forest and Stream some valuable "Notes on the Natural History of Southwestern Texas," from which we take the following account of the "vinagrone" (big vinegar, so called on account of the pungent secretion it ejects), an arachnidan found in the vicinity of Fort Stockton. In general appearance it resembles a large scorpion, though belonging to a different family. From the head to the commencement of the tail the adult vinagrone is full two inches long; in breadth it measures about three-quarters of an inch. The thorax and head are amalgamated, while the thorax and abdomen are separated by flexible tissue. The legs are six in number, all attached to the thorax. The trunk and head are protected by a single dorsal plate; the abdomen has sixteen distinct dorsal and ventral laminæ, which overlap; they would form continuous rings, were it not that they are curiously separated laterally by elastic tissue. This division of the abdominal rings affords considerable flexibility, and gives the insect the appearance of bearing about him an old-fashioned bellows. From the terminal, dorsal, and ventral plates is given off a series of rings, which, after the third one, are fused into a stiff spike or tail, that is usually three-fifths of the length of the entire body, and covered with short bristles like the legs. This is not a sting, nor does it seem to be the duct through which the secretion is ejected. It appears to be used principally as a posterior feeler, and sometimes as an aid to locomotion.

From the head are given off two powerful brachials, each having four articulations. They resemble the arms of a scorpion, and terminate in sharply-curved pincers. The threatening manner in which they are opened and stretched out, when the insect is enraged or is seeking for its prey, almost makes one shudder. But the brachia are not its only means of offense. Beneath the frontal plate are two long, incurvated fangs. Connected with these are two sacs, that, by pressure, exude drops of greenish liquid over the fangs, and in them undoubtedly resides the true venom of the insect.

Of the bite of this animal the author writes: "We have no good proof that the bite of the vinagrone would be fatal to man,