266 



THE POLISHED ROCKS OF ROCHESTER. 



probable that a large surface is polished. In several places the 

 polish stops, for no reason that can be assigned. On the cast 

 side of the river, the polished surface has not been found over one 

 fourth of a mile distant, till yesterday I discovered it about a mile 

 east of it. The polish is not on the same level, but passes over 

 the outcropping edges of the strata, rising several inches in a foot 

 or two, and showing the strata worn at the edge very thin ; yet the 

 polish is as perfect as on the level, and the rock shows no signs 

 of its stratification till it is broken up. It is sometimes curved 

 too in a few inches, as if the surface had been worn into a shal- 

 low hollow by the polishing surface. From the Genesee Valley 

 Canal, where the rock is polished, the surface rises to the west, 

 perhaps twenty feet in one hundred rods, and the polished sur- 

 face has been found every few rods by the digging of wells or 

 cellars. 



The polished surface has sometimes only a thin ^covering of 

 earth upon it, and is sometimes under earth, ten, tw^enty, and thirty 

 feet or more deep, just as it has been heaped upon it by diluvial 

 agency. This erratic group is sand, clay, gravel, and bowlders 

 of the primitive rocks, which must have come a great distance, 

 and of sandstone, which has been moved only a few miles, and 

 of geodiferous limestone, which is still less removed from its 

 proper place. The former set of bowlders seems to be buried at 

 a greater depth than the others. The striae and furrows show that 

 large and sharp bodies must have been moved on the surface. 

 May not the polish have been first WTOught by earth and sand, 

 and the furrows effected by that diluvial action which brought on 

 the erratic group far from the north ? 



