Page:Popular Science Monthly Volume 42.djvu/734

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of the ground. It is perhaps enough to say that the coal measures to which coal is confined in Arkansas lie far to the north of Hot Springs, and that the hot waters come up through Silurian rocks which contain no coal. Of the theory that heat may be produced by chemical action, it may be said that the water itself gives no evidence of its having received its heat in this way, its chief foreign constituent being carbonate of lime. So far as the geology of the region is concerned, if there were no hot water in the vicinity none would have been anticipated on geologic grounds alone. Notwithstanding a writer at the beginning of the century mentioned having seen a volcanic outburst and streams of molten rock near Hot Springs, there is no evidence of such recent eruptive action, which could not have taken place without leaving readily recognizable traces. There are, however, eruptive rocks near Hot Springs, although they certainly were not thrown up during the last hundred years; and it is probable that the heat of the water is derived from its having come in contact with hot rocks, the cool edges of which may or may not be exposed at the surface.

Ancient Outlet of the Great Lakes.—Among the latest geological observations of Prof. G. F. Wright is the discovery of a former outlet of the Great Lakes through Lake Nipissing and the Mattawa River to the Ottawa. It has long been recognized that an elevation of less than fifty feet at Niagara or a depression of an equal amount at Chicago would cause the lake waters to flow into the Mississippi instead of the St. Lawrence. Recent railroad surveys have further shown that a subsidence amounting to only a trifle more than a hundred feet would turn the current from Lake Huron through Lake Nipissing and the course already mentioned. Prof. Wright has discovered evidence that this condition at one time prevailed. Lake Nipissing is scarcely seventy feet above Lake Huron, and empties into it through French River. The western extremity of Trout Lake, the source of the Mattawa, is less than three miles from North Bay on Lake Nipissing, and is separated by a wide, swampy channel which is only about twenty-five feet above the level of either lake. It is large enough to conduct the waters of the Great Lakes over into the present water-shed of the Ottawa when called upon to do so. "On looking for more positive evidence, we find it in a clearly defined shore-line of well-rounded pebbles extending upon the north side of the channel from one lake to the other, and at a uniform height of about fifty feet above the connecting channel. This shoreline is as well defined as that on the banks of the Niagara River, just west of the present cataract. Such a deposit could not have been formed along this connecting depression except by a stream of vast size passing from Lake Nipissing into the Mattawa. It is, however, on going down to the junction of this outlet with the Ottawa that the most positive and striking evidence is seen. For ten miles above the junction signs of the old river terraces are more or less visible high above the present stream; but at the junction there is an accumulation of river deposits, unparalleled, probably, by anything else in the world. The lower angle of the junction between the two streams is filled to a height of eighty feet or more above the present water level with a bowlder-bed about half a mile in width, and extending up the Mattawa for nearly a mile, where it shades off into finer material. On the upper angle the Mattawa is bordered by a terrace equally high, but consisting for the most part of fine gravel." The accumulation is clearly a terrace and not a simple glacial moraine; and that it is a delta brought down by the Mattawa and not by the Ottawa is shown by the fact that it has dammed the latter stream, producing in it deep water above and rapids below, according to the well-known law of river bars.

Traveling and Camping in Egypt.—Dr. Frederick Peterson, of this city, recommends winter camping in Egypt as a hygienic measure. He finds it something luxurious, and says: "I have camped out on shooting expeditions in Nebraska, Dakota, and other Western places, and endured hardships that I should not care to experience again. But in Egypt, where labor and carrying cost next to nothing, where everything in the way of furniture and supplies can be stored away somewhere on a camel; where every day can be foreseen to be rainless and beautiful, life in tents becomes a pleasure. It is al-