188 NATURE STUDY IN SCHOOLS. 



where sand, gravel, or other glacial debris has been recently removed. Such 

 an one is to be found on Lowell Ave. in Newtonville, near the stone 

 crusher. Here a section of rock has been exposed by the removal of grav- 

 el. The rock is serpentine, and is in the form of a sloping cliff about twenty- 

 five feet high and a hundred feet long. The cliff lies parallel with the ave. 

 which runs about north and south. 



An examination of the surface of this newly exposed ledge shows furrows 

 in the rock an inch or an inch and a half deep. Further examination of 

 these scratches shows that they were made by a rough surface, moving very 

 nearly, but not quite parallel with the face of the cliff, and striking it a 

 little obliquely. 



Another newly exposed rock-surface ( a cliff of slate by the roadside at 

 the back of a gravel-pit) is to be seen at Newton Center, a little over two 

 miles from this serpentine quarry. The cliff is about fifteen feet high and 

 faces the north, and an examination of it shows that the glacier struck it 

 directly on its face. Slate is softer than serpentine, partly on this account, 

 and partly on account of its situation, the scratches here are deeper and wider 

 than in the former ledge. The upper surface of this cliff is smoothly 

 worn into huge scallops by the action of the moving ice. 



An inspection of these two cliffs shows the general direction in which 

 the glacier moved. While it passed obliquely along the side of the serpentine 

 cliff, which runs nearly from north to south, it struck the slate cliff, which 

 has a northern exposure, full on its face It is thus evident in both 

 places that the ice was moving from the north-east to the south-west. 



Between this slate ledge and the village of Newton Center, is a freshly- 

 exposed bed of conglomerate rock, or pudding stone. This shows admirably 

 the powerful grinding action of the glacier. Here the hard, flint-like pebbles 

 which form the pudding-stone are ground down, so that they are often exposed 

 in perfect sections ; while the rock in general is nearly as polished as a glazed 

 surface. 



A visit to these places will amply repay those interested in the study of 

 glacial action. 





