Page:Popular Science Monthly Volume 49.djvu/295

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Some New Observations on Underground Temperatures.—Some recent observations on underground temperatures are described in the December number of the American Journal of Science by Prof. A. Agassiz. He says: "For several years past I have, with the assistance of Mr. Preston C. F. West, been making rock temperature observations as we increased the depth at which the mining operations of the Calumet and Hecla Mining Company were carried on. We have now attained at our deepest point a vertical depth of 4,712 feet, and have taken temperatures of the rock at 105 feet; at the depth of the level of Lake Superior, 655 feet; at that of the level of the sea, 1,257 feet; at that of the deepest part of Lake Superior, 1,663 feet; and at four additional stations, each respectively 550, 550, 561, and 1,256 feet below the preceding one, the deepest point at which temperatures have been taken being 4,580 feet. We propose when we have reached our final depth, 4,900 feet, to take an additional rock temperature, and to then publish in full the details of our observations. In the meantime it may be interesting to give the results as they stand. The highest rock temperature obtained at the depth of 4,580 feet was 79° F.; the rock temperature at the depth of 105 feet was 59° F. Taking that as the depth unaffected by local temperature variations, we have a column of 4,475 feet of rock with a difference of temperature of 20° F., or an average increase of 1° F. for 223·7 feet. This is very different from any recorded observations. Lord Kelvin, if I am not mistaken, giving as the increase for 1° F., fifty-one feet, while the observations based on the temperature observations of the St. Gothard Tunnel gave an increase of 1° F. for sixty feet. The calculations based upon the latter observations gave an approximate thickness of the crust of the earth in one case of about twenty miles, in the other twenty-six. Taking our observations, the crust would be over eighty miles, and the thickness of the crust at the critical temperature of water would be over thirty-one miles, instead of about seven and 8·5 miles as by the other and older ratios. . . . The holes in which we placed slow registering Negretti and Zambra thermometers were drilled, slightly inclined upward, to a depth of ten feet from the face of the rock and plugged with wood and clay. In these holes the thermometers were left from one to three months. The average annual temperature of the air is 48° F.; the temperature of the air at the bottom of the shaft was 72° F." A possible source of error in these observations arises from the free access which the surface air has to the mine, and the probable effect which it must exercise on the rock temperature for many feet about it. This is, of course, also true of the previous observations, conducted in mines or tunnels. Another feature which would perhaps introduce a source of error is the close proximity of the enormous mass of water in Lake Superior. It seems probable that the rock temperature in this whole region is largely modified by the vast body of water in the lake system.

The Northern Appalachians.—A concise, satisfactory summary of the characteristics of the northern Appalachian Mountain ranges is given by Mr. Bailey Willis in a paper published in the series of Monographs of the National Geographic Society. Instead of being marked by a central crest, as is usually the case, these ranges are characterized by a central zone, the surface of which is lower than the ranges on either side. This zone is a very complex valley, or series of valleys, and is known by different names in different sections of its length of a thousand miles. Two principal ranges bound it—one on the southeast, generally known as the Blue Ridge, and the other on the northwest, known as the Alleghany Front. They extend in two nearly parallel lines about seventy-five miles apart, and have each its special characteristics. The rivers flow either to the Atlantic or to the Ohio River. The divide between these groups of streams is winding and often inconspicuous, and has no definite relation to the