ON THE GLACIAL POTHOLE IN THE NATIONAL 



MUSEUM 



By GEORGE P. MERRILL 



For several years the department of geology of the National 

 Museum was on the lookout for a desirable object of the nature indi- 

 cated by the above title and of such dimensions and so situated as 

 to allow its removal and installation in the National Museum. In 

 the summer of 1884 the one finally obtained was " located," but it 

 was not until 1892 that conditions favored the attempt to remove 

 it. The supervision of the work was entrusted to Dr. O. C. Far- 

 rington, to whom I am indebted for the account of its extraction 

 given below. The rock in which the pothole occurs is a gray, white- 

 banded, strongly foliated, micaceous gneiss, standing nearly on 

 edge, with the hole eroded parallel with the foliation. These fea- 

 tures are shown in the accompanying illustration (plate xxxi). It 

 is scarcely necessary to state that the parallel flutings on the out- 

 side of the block were caused by the drills during the process of ex- 

 traction. Although somewhat shattered by the jar of blasting, as 

 stated by Dr. Farrington, the injury was easily remedied by a little 

 cement, and the specimen as it stands to-day is one of the most strik- 

 ing in the department. The total weight of the specimen is about 

 4000 pounds. 



Following is a transcript of the label : 



GLACIAL POTHOLE 



Riggsville Landing, Georgetown, Maine, 60,880. Collected for the 

 Museum under the direction of O. C. Farrington. 1893. 



" Besides its proper and characteristic rock erosion, a glacier is 

 aided in a singular way by the cooperation of running water. 

 Among the Alps, during the day in summer, much ice is melted, and 

 the water courses over the glaciers in brooks which, as they reach 

 the crevasses, tumble down in rushing waterfalls, and are lost in the 

 depths of the ice. Directed, however, by the form of the ice passage 

 against the rocky floor of the valley, the water descends at a par- 

 ticular spot, carrying with it the sand, mud, and stones, which it may 

 have swept away, from the surface of the glacier. By means of 

 these materials it erodes deep potholes (moulins), in which the 



