Streams of gas issue from below, sometimes rising through the water but more frequently hissing and gurgling from small openings in the pitch above water level. It appears to be chiefly sulphuretted hydrogen, smelling strongly of that gas and instantly blackening a silver coin laid among the bubbles. When inflamed it burns with a pale yellowish flame. The surface of the pitch is whitened in places by a deposit of sulphur. The temperature of one of the streams of gas was 97° Fah., the highest heat which I observed upon the lake. The water in some of the crevices was 95°. In such cases it appeared to be rising at one end of the opening, flowing along, and descending at the other. I have no doubt that the mere surface of the pitch is sometimes heated by the sun to a higher degree than this. But the copious streams of gas would certainly indicate the fact if a much higher heat existed at a moderate depth below. The pitch where most fluid had a temperature of only 95°. It is evident that the bitumen does not owe its fluidity in any great degree to heat. It is true that the already hardened pitch may be melted by a sufficient heat, but that which is already fluid remains so at all ordinary temperatures. Wherever it oozes out in streams it flows down over the hardened surface into the nearest channel of water (which may have a temperature not above 85°), where it creeps along the bottom in a stream that looks like a huge serpent. The fluidity of the pitch is evidently owing to the oily matter which it contains. The whole thing seems more like a vast fountain of coal tar than anything else. The gradual hardening which has evidently taken place is due to oxydation and evaporation of the less fixed ingredients,-a process which the revolving motion heretofore described must greatly facilitate. In one of the star shaped pools of water, some five feet deep, a column of pitch had been forced perpendicularly up from the bottom. On reaching the surface of the water it had expanded into a sort of center table about four feet in diameter but without touching the sides of the pool. The stem was about a foot in diameter. I leaped out upon this table and found that it not only sustained my weight but the elasticity of the stem enabled me to rock it from side to side. Pieces torn from the edge of this table sank readily showing that it had been raised by pressure and not by its buoyancy. The vicinity of the pitch with its strong odor seems to give no more offense to animals than its presence in the soil does to vegetation. Numerous fishes ten or twelve inches long were seen in the water on the lake. An alligator shuffled off from one of the areas at my approach. In two instances I scared birds resembling night hawks from their nests or rather from their eggs which were deposited upon the naked pitch. In the course of several days spent in examining the lake and the region around it I walked several miles along the sea-shore both to the northward and to the southward of the lake. То the southward the shore is made up of bold cliffs upon which the sea is making rapid inroads. The strata consist of indurated clays of brilliant red and yellow colors. They present also thick veins of porcelain jasper. Strata of loosely coherent sandstones also abound. These are more solid and durable where they are impregnated with bitumen which acts as a cement. Rounded pebbles of pitch and porcelain jasper form a beach at the foot of the cliffs. About a mile and a half south of the lake I observed numerous beds of slightly indurated clay filled with the remains of leaves and vegetation. A little further on appears a bed of brown coal and lignite about twelve feet thick. It has such a dip and direction that if continuous it would pass under the lake at a great depth. But the strata are here much contorted and some even thrown into upright positions. Pebbles of pure asphaltum are thrown up by the waves at this point and not far off the beach is blackened by brilliant titanic iron sand. Nearer the lake and to the southwest of it, a large spring of petroleum breaks out under the sea. The escape of gases from this vent is sometimes so violent as to spout a column of water several feet high. I passed over the place in a boat but at the time there was no ebullition although a strong odor of bitumen pervaded the sea breeze and acres of the sea were iridescent with the floating oil. The rocks on the beach opposite were varnished of a bright glossy black by the petroleum. I filled a bottle with it by skimming it up from the water with a palm leaf. Many springs of petroleum occur in the interior, within a few miles of the lake. Two veins of pure asphaltum enclosed in clay were discovered about three-fourths of a mile from the same place. They were soon however exhausted, having yielded some twenty tons of the mineral sufficiently pure for varnishes. From the point where the large spring of petroleum breaks out under the sea, at least three miles of the shore to the northward consists mainly of streams of pitch from the lake. There are a few intervals of sandstone and clays where elevations have diverted the bituminous currents. But all the most prominent head-lands are those which are defended by the indurated pitch. This material has in fact flowed out to a considerable, though as yet unknown, distance under the sea. About a mile to the northward of the lake another bed of brown coal crops out upon the shore. It is about twenty feet thick. Other and perhaps much thicker beds may exist in the vast mass of stratified materials which make up the bulk of the island. From the occurrence of such considerable accumulations of vegetable matter so situated as apparently to pass under the lake, it seems reasonable to regard them as the source of the pitchy matter which rises in such quantity there. Indeed many pieces of wood may be observed in the beds of brown coal which differ in no respect in their appearance from many of the pieces thrown up in the lake itself. These beds of vegetable matter are probably undergoing a slow distillation by volcanic heat. It is true there are no evidences of volcanic eruptions in the vicinity of the lake nor any materials of volcanic origin scattered on the beach except perhaps the titaniferous iron sand. But at Cedras, twenty miles to the southward, there are active mud volcanoes. I did not have opportunity to examine them or to ascertain their character minutely. But the fact of their existence as well as the disturbed condition of the recent strata, together with the proximity of the island to the coast of Cumana where earthquakes are frequent and severe, appears sufficient to show that the island is not entirely free from volcanic action. Various attempts have been made to apply the inexhaustible store of bitumen afforded by the lake, to some useful purpose. Mixed with sand and pebbles it is much used for pavements and the ground floors of houses at Port au Spain, a purpose for which it is admirably adapted. It has been employed to advantage as fuel by the American steamers plying on the Orinoco. It is thrown in the furnaces among the wood, fusing too readily to be used alone. With ten per cent of rosin oil it forms an excellent pitch for vessels. The Earl of Dundonald has purchased a large tract of the pitch lands including twenty six acres of the lake and has instituted various experiments with the view of substituting the bitumen for India rubber and Gutta percha in the manufacture of water proof fabrics, covering of telegraph wires, &c. Judging from the specimens of water proof cloth, tubing and telegraph wire which were shown me by his agent at Port au Spain, (Mr. C. F. Stollmeyer,) these efforts bid fair to be quite successful. It seems only necessary that the required amount of intelligent enterprise should be directed to the subject in order to render this wonderful reservoir of bitumen a source of great individual profit and of essential service to mankind. ART. XIV.—The Harrison Tornado, Ohio, February 14, 1854. It is of interest in illustration of the subject of storms, to notice briefly the Harrison tornado, as its action differs in some respects from the Brandon storm. Many of its operations were chronicled as being of such a wonderful and unheard of character, that the writer was induced to visit the scenes of its ravages, to examine and record the facts, of whatever nature they might be. During no season since, perhaps, the settlement of the state, have so many visitations of the kind occurred; and the opportunity afforded has been uncommonly favorable for investigating the phenomena of these storms. The tornado under consideration, commenced, as far as can be learned, in Dearborn Co., Ia., 10 or 12 miles west of Harrison, in North Latitude 39° 10' and West Longitude 70°. Its course was N. 72° 32′ E., ravaging the country, at intervals for 50 miles. Its most marked characteristic was a diffuse and feeble action at the circumference, and intense energy at the axis. Occasionally it struck objects along its axis with the spite of a fury; closely approximating in its sudden and destructive effects, to the blast from a huge cannon. The most striking examples of its violence were found at the Graham place. West of Harrison the country was very much broken; and generally wherever the tornado ascended a hill or crossed its top, it left the forest untouched; but the moment it began its descent, everything fell before it. It frequently rose from the earth, or was so broken up by the obstacles encountered, that extensive tracts were passed without injury. Its destructive effects were mainly confined to a path varying from 200 to 600 feet in breadth. At the Graham place it was three-fourths of a mile broad; at Mr. Wakefield's woods 66 rods; and at Dr. Bowles, from the extreme point on the right, where fences in the open fields were prostrated, to the left where trees were thrown down, must have been a little more than half a mile. Careful observations were made at the Graham place, by the writer assisted by the Rev. M. Golliday of Harrison; also at the latter place; and at Mr. Wakefields; and a somewhat hasty examination at Dr. Bowles. The Graham house (I) stood in the edge of a forest which extended to the west, with open ground on the east. West of the house (see plot) about 4th of a mile, a narrow and deep valley runs north and south. Lateral valleys intersect this nearly at right angles from the east. These are also deep and narrow gorges, extending about one-fourth of a mile back from the main valley, forming sharp and well defined ridges between them. At the SECOND SERIES, Vol. XX, No. 59.-Sept., 1855. 21 |