136 G. II. Stone — Wind Action in Maine. 



on hillsides above the level of the valley-drift and most of 

 them were on the south side of the river on slopes well ex- 

 posed to the north and northwest winds. In fields and by the 

 road-sicles in Bethel, where the bowlders had probably never 

 been disturbed by plowing, I made note of the positions of the 

 polished faces of hundreds of the bowlders. The polished sur- 

 faces were turned in every direction, but more faced the west 

 and northwest. Dr. True's observation that one face of these 

 bowlders is usually unpolished was verified, though in one case 

 a bowlder was found polished on all faces. In the majority of 

 cases this unsculptured face was the lower face. In the year 

 1880, I deposited specimens of the Bethel bowlders in the cabi- 

 net of the Boston Society of Natural History, and submitted 

 them to several glacialists for examination. But during all of 

 this time none of us obtained any inductive clue to the mys- 

 tery — the cause of the peculiar carvings. In 1881 I removed 

 to Colorado and for the first time saw in the field the sand- 

 sculptured bowlders so common in the arid regions, and their 

 forms were seen to be the same as those of the Bethel bowlders. 

 Here at last was an opportunity to leave speculation for a valid 

 induction. At once several theories were suggested as account- 

 ing for the peculiar shapes of the Bethel bowlders, but it has 

 been necessary to wait for several years in order to determine 

 by observations in the field which one is the true hypothesis. 

 Three of these alternatives are here stated and briefly dis- 

 cussed because they bear on the question of the causes of the 

 shapes of the drift materials, and this is sure to be a pressing 

 and significant question for glacialists to solve. 



1. These bowlders maj^ have been sand-carved by the wind 

 in their present positions, and recently. If true, this hypothe- 

 sis could easily be verified by finding the process now in op- 

 eration. 



2. They may have been sand-carved by the dashing of the 

 rain chiefly. That this is a cause of sand-carving there can be 

 no doubt; but if such extraordinary forms as those at Bethel 

 are due to this cause, then similar surfaces ought to be com- 

 mon everywhere, unless there is something in the Bethel bowld- 

 ers fitting them to receive or preserve such polishing better 

 than other bowlders. But on the other hand they are only 

 ordinary drift bowlder's, representing various common rocks ; 

 they are neither harder nor softer than many others, nor can 

 they resist weathering any better. Many of them are of a very 

 feldspathic granite, while in others quartz predominates. 



3. They may have been sand-carved by glacial streams. 

 Whenever swift sediment-laden streams impinge obliquely 

 against a rock surface, that surface is carved into tremulous 

 grooves showing many sub-conchoidal depressions very nearly 



