GEOLOGY IN NATIONAL MUSEUM MERRILL. 283 



GLACIERS AND GLACIAL PHENOMENA. 



The general plan of this exhibit is as follows: 



I. Views illustrating living glaciers, icebergs, etc. 



II. Kelief map of the United States showing the ice 

 sheet of the glacial epoch in its lobate stage. 



III. Illustrations of glacial phenomena (pis. 12 and 13). 



IV. Specimens illustrative of the transporting and erod- 

 ing power of glaciers. 



V. The possible economy of glaciers as illustrated in the 

 utilization of glacial materials, clays, etc., and the stripping 

 of rock masses of their decomposition products, rendering 

 sound material available for quarrying. 



VI. The destructive effects of glaciation, as illustrated by 

 fields covered by drift boulders and other glacial debris; 

 the stripping of the surface of soils, and the burial of 

 forests. 



Among the drifted materials are boulders from various altitudes 

 up to within a few feet of the summit on Mount Washington. These 

 were all foreign to the mountain, and their presence fixes the min- 

 imum thickness of the ice sheet, at this point, at 6,000 feet. 



There are other series of drift boulders of which the parent ledge 

 is known, such as the peridotite from Cumberland, R. I., the jasper 

 conglomerate from Leroy Township, Canada, and the native copper 

 from Lake Superior. Examples of the latter are shown which were 

 found as far to the south as Oxford, Ind., and of the conglomerate 

 at various distances up to 600 miles from their source. 



The relief map mentioned (pi. 14) which was originally prepared 

 for the World's Columbian Exposition at Chicago in 1893, bears the 

 following explanatory label : 



Model of the United States 



showing the theoretical restoration of the Ancient Ice-sheet at 

 the stage of the Glacial Period following the Main Silt 

 Epoch. Constructed from data furnished by T. C. Charnber- 

 lin and associates of the U. S. Geological Survey; the outline 

 of the ice follows the outer terminal moraine next north of 

 the main silt deposits, and probably does not represent a 

 strictly synchronous stage throughout, as later advances of 

 the ice at some points overrode earlier ones, making it difficult 

 to trace a perfectly synchronous line. The slope of the sur- 

 face of the ice is based on an adaption of that of Greenland, 

 as given by Nansen. 



The scale of the model is 1 inch to 40 miles. It shows 

 the correct curvature at sea level, and is a section of a globe 

 162 feet in diameter; elevation and depression above and 

 below sea level exaggerated five times. 



