326 GLACIAL GRAVELS OF MAINE, 



excavated by the Indians. That they are glacial potholes is proved by the 

 following- facts : 



One of the potholes near Riggsville is situated about 1^ miles south- 

 ward from that place, on the shore of Robin Hoods Cove. The pothole is 

 covered by about 1 foot of water at time of ordinary hig-h tide. It is near 

 10 feet in depth; its avei'age diameter is -4 feet at the top and 6 feet at the 

 bottom. It is excavated in a little shelf of rock on the side of a rather steep 

 ledgy hill, about 40 feet high. Within a few rods this hill slopes in the 

 opposite direction from the shore, down to the valley of a small brook 

 which enters the cove about one-eighth of a mile north of the pothole. 

 The ground slopes down from the hill in all directions, so that the only sur- 

 face drainage that ever could reach this pothole must have come from a 

 slope only a few rods long. The rock is a compact gneiss, with no veins 

 or dikes at this place and no fault or fracture. I could find no other sign 

 of running water in the vicinity. There were stones in the bottom of the 

 hole ihat could be moved around by an oar, but I had no means of getting 

 them out, and it was impossible to see more than 2 feet into the black water. 

 Robin Hoods Cove is here near one-fourth of a mile wide, and contains no 

 islands or rocks to cause a tidal race. About one-eighth of a mile north of 

 Riggs Landing are two potholes at an elevation of about 60 feet above the 

 sea. The one situated at the southwest is about 4 feet in diameter and 5 

 feet deep. The other is about 6 feet in diameter and 10 feet deep. Both 

 are nearly round, and tlie walls are quite smooth. The layers of gneiss, 

 tilted lip at high angle, are continuous, except where interrupted by the 

 holes. The same layers can be readily traced on opposite sides of the holes. 

 There is no sign of veins or fractures. In the potholes were rounded peb- 

 bles and bowlders, one of them 3 feet in diameter, well rounded at the 

 edges and angles. Some of the rounded stones had been taken out by 

 previous explorers. The holes are situated on the southern slope of a hill 

 of gneiss that rises 150 feet (by aneroid) above the sea. The hillside shows 

 much bare rock and is broken by numerous hillocks and small valleys. We 

 reach the top within about one-fourth of a mile from the shore. All the 

 surface drainage that ever could have reached the holes came from this hill- 

 side, and that, too, on an irregular surface where no single valley exists to. 

 direct the flow of water to these holes. 



About one-half mile north of Riggs Landing there is a pothole on the 



