Page:Popular Science Monthly Volume 17.djvu/184

172 it probably nowhere exceeds five thousand; that in depths of about two thousand fathoms there is the globigerina ooze, a substance resembling chalk, formed of the shells of living organizations that existed on the surface of the sea, and sunk to the bottom on the death of the animal. This ooze occupies considerable portions of the bed of the Atlantic, Pacific, and Southern Oceans. In depths below three thousand feet an extremely reddish clay is found, which is apparently the decomposition of submarine volcanoes and of decomposed organisms. What is at present forming a great depth does not correspond, either in structure or chemical composition, with any known geological formation, and warrants the belief that none of the older formations of the globe were laid down at such great depths. Sir Wyville Thomson adopts the opinion of Professor Dana, of Yale College, that the eruptions which originated the mountain-chains that form the skeleton of our present continents, and the depressions occupied by our present seas, arose from the cooling and contraction of the crust of the earth at a period more remote than the deposition of the earliest fossiliferous rocks.

Dr. Kroll, of Göttingen, has also been engaged in investigating the depth of the ocean, and estimates the mean depth at 1,877 fathoms, an estimate not very much below that of Sir Wyville Thomson.

In meteorology the most notable phenomena have been the very marked changes of the ordinary temperature in different parts of the world, particularly in western Europe, in certain parts of Asia, and in the eastern portion of the United States. It has been marked in Europe by winters of increased severity and an undue prevalence of moisture in the spring and summer, attended by very disastrous consequences to agriculture in Great Britain, France, and some other countries. The last winter on the European Continent, as well as in Great Britain, has been one of the severest upon record. In France the thermometer has never been so low since 1795, with the exception of one year, 1871, when the cold, however, was but of short duration. In Switzerland and southern Germany, especially in the mountainous parts, the severity of the winter has been exceedingly disastrous; while in this country the winters—especially the present winter—have been of unusual mildness in all the States east of the Mississippi.

In Asia the changes in the ordinary temperature have been equally remarkable. In the mountains of Cashmere there was a snowfall last winter extraordinary even in that mountainous region. In certain places it snowed uninterruptedly and heavily for ten continuous days, the snow upon the level plains being from thirty to forty feet deep, and in some of the mountain-passes it was piled up to a height of one hundred and fifty feet, and in others to two hundred and fifty feet.

Various conjectures have been advanced as to the cause of this unusual change of temperature. A writer in the "New York Herald" attributes the fact that the spring and summer in Europe was