76 



GEOLOGY OF OHIO. 



BEARINGS OP GLACIER FURROWS. 



The glacial markings on West Sister Island, as shown by Mr. Gilbert, 

 demonstrate that the motion of the ice was from east to west. In the 

 Waterlime of which this island is composed are numerous balls of chert 

 which have been exposed to the action of the glacier. We now find these 

 projecting from the general surface much more strongly on their eastern 

 than on their western sides, and from each a ridge or trail of limestone 

 which they have protected from erosion runs off toward the south-west. 

 Around the eastern base of each nodule is a deeply excavated furrow, 

 which leads off on either side of the ridge just mentioned. Occasionally 

 these flint nodules are cracked and battered, as they could hardly have 

 been except by the action of bowlders, which, held by the ice, had come 

 in contact with them. The exceeding fineness of the sculpture around 

 these nodules, as well as in many of the longitudinal furrows, prove that 

 the erosion was generally done, not by stones held in the ice, but rather by 

 sand, which, frozen into the plastic ice, was capable of executing any sort 

 of carving and modeling with the greatest accuracy. The glacial furrows 

 on Kelly's and Put-in-Bay Islands have been often referred to, and are 

 more surprising for their magnitude, extent, and variety than any 

 others known in the country. In the fossiliferous limestone of Kelly's 

 Island the glacial surface is thickly mottled with sections of corals and 

 other fossils. These are ground down, often as nicely as they could be 

 done by hand, and show distinctly that sand, under the ice, must have 

 been the grinding agent. In many localities on these Islands the gla- 

 cial furrows curve around any prominent point or rock mass which was 



