258 THE POPULAR SCIENCE MONTHLY. 



matter is necessarily intercepted by large and deep lakes, the 

 presence of this Alpine alluvium immediately beneath the glacial 

 debris 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 considera- 

 tions set forth in this paper show such a number of distinct lines 

 of evidence, all converging to establish the theory of the ice ero- 

 sion 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. 



QERARD 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 Abb^ Rend Just Haiiy, author of the famous sys- 

 tem 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 priva- 

 teer ; confined for some time at Dunkirk ; returned to Paris ; and 



