Page:Popular Science Monthly Volume 5.djvu/395

 here," says the author, "as excluding from the possible causes of the light the luminosity of gaseous matter, either spontaneous, or due to electrical discharge. The supposition that the light is reflected from masses of gas, or from globules of precipitated vapor, is not to be entertained, since, as Zöllner has shown, such globules in otherwise empty space must evaporate completely, and a gaseous mass would expand until its density became far too small to exert any visible effect upon the rays of light."

From this it follows that the light must be reflected from matter in the solid state, that is, from innumerable small bodies (meteoroids) revolving about the sun in orbits crowded together toward the ecliptic.

The Great Lava-Flood of the West.—Prof. Joseph Le Conte, of the University of California, visited, during the summer of 1873, the central and eastern portions of Oregon, a vast lava-covered region, and published the results of his observations in the American Journal of Science for March and April, 1874. Using the word lava as synonymous with eruptive rocks, he says that between 200,000 and 300,000 square miles of surface is one field of lava. It is probably the most extraordinary lava-flood in the world. Commencing in Middle California as separate streams, in Northern California it becomes a flood flowing over and completely mantling the smaller inequalities, and flowing around the greater inequalities of surface; while in Northern Oregon and Washington it becomes an absolutely universal flood, beneath which the whole original face of the country, with its hills and dales, mountains and valleys, lies buried several thousand feet. It covers the greater portion of Northern California and Northwestern Nevada, nearly the whole of Oregon, Washington, and Idaho, and runs far into Montana on the east, and British Columbia on the north.

This enormous mass of matter evidently arose through fissures, and flowed until the streams or masses met, forming an almost continuous sheet. The Cascade Range of mountains seems to have been a source of immense overflow.

The area covered by this overflow cannot be less, says Prof. Le Conte, than 100,000 square miles, with an average thickness of about 2,000 feet, but having a thickness in some places of 3,700 feet. The statement, which seems an extraordinary one, is sustained by the extensive observations of Prof. Le Conte. The Columbia River cuts through the Cascade Range in a gorge a hundred miles in length, with perpendicular cliffs. The cascades of the river are at the axis of the range, and the cliff's here are 2,500 to 3,800 feet above the river-surface, and are composed of lava, tier upon tier, from top to bottom. Considering surface erosion, 4,000 feet is regarded as a moderate estimate for the original thickness of the lava-flood at this place.

But the entire thickness of the lava has been cut through, and the surface revealed on which the flood was originally formed. Here, at the river's surface, underlying the mountains of lava, are remains of ancient forests, and evidences of interesting geological changes.

There occurs at the river's edge, and about fifteen feet upward, a layer of coarse conglomerate; on this, a layer which appears to have been a dirt-bed, or old-ground surface. On this surface were found two silicified stumps, with their roots spread out, one of which was two feet in diameter, the roots reaching over an area twenty feet in diameter. Trunks of other trees were seen. Over this was a layer of stratified sandstone, with beautiful impressions of leaves of several kinds of forest trees. Upon this lies about 100 feet of conglomerate, resembling drift, in the bottom of which were found trunks and branches of oaks and conifers. Upon the conglomerate the lava lies in columnar masses to a height of 3,300 feet.

The geological age of the wood and leaf-bearing stratum is believed to be miocene, or middle tertiary, and, if so, the lava-flood began to occur during or after the miocene.

Why Paints crack and peel.—A writer in The Hub thinks that the cause of paint cracking and peeling is to be found in the water which is contained in linseed-oil, as it comes from the hands of the manufacturer. He made the experiment of boiling linseed-oil by the heat of steam, until all