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THE POPULAR SCIENCE MONTHLY.

matter is necessarily intercepted by large and deep lakes, the presence of this Alpine alluvium immediately beneath the glacial débris at the foot of the lake indicates that the lake did not exist in pre-glacial times, but that the river Rhone flowed from the Alps to Geneva, carrying with it the old alluvium, consisting of mud, sand, and gravel, which it had brought down from the mountains. Still more conclusive, however, is the fact that the three special features which have been shown to indicate erosion rather than submergence are present in this lake as fully as in all other Alpine valley lakes and unmistakably point to the glacial origin of all of them.

On the whole, I venture to claim that the facts and considerations set forth in this paper show such a number of distinct lines of evidence, all converging to establish the theory of the ice erosion of the valley lakes of highly glaciated regions—a theory first advocated by the late Sir Andrew Ramsay—that that theory must be held to be established, at all events provisionally, as the only one by which the whole body of the facts can be explained and harmonized.—Fortnightly Review.

[Concluded.]

 

SKETCH OF GERARD TROOST.

GERARD TROOST, one of the founders and first President of the Academy of Natural Sciences of Philadelphia, was born at Bois-le-Duc, Holland, March 5, 1776, and died in Nashville, Tenn., August 14, 1850. He attended the Universities of Leyden and Amsterdam, devoting special attention to chemistry, geology, and natural history; received the degree of Doctor of Medicine from the University of Leyden, and that of Master in Pharmacy, in 1801, from the University of Amsterdam. He practiced his art for a short time at Amsterdam and the Hague; served in the army as a private soldier, and at another time as an officer of the first class in the medical department; and during these periods of service was wounded in the thigh and in the head. In 1807 he went to Paris, under the patronage of Louis Napoleon, King of Holland, to pursue his studies, and then he became the pupil and associate of the Abbé René Just Haüy, author of the famous system of crystallography. He traveled in France, Italy, Germany, and Switzerland, and collected a valuable cabinet of minerals, which was purchased by the King of Holland. In 1809, this king appointed Troost to accompany, in a scientific capacity, a naval expedition to Java. He was captured by an English privateer; confined for some time at Dunkirk; returned to Paris; and