GLEN ROY, IN SCOTLAND. 
35 
inequalities have been completely levelled and 
its surface lias become glossy. Any marble 
mantel-piece may serve as an example of this 
kind of glacier-worn surface. 
The levelling and abrading action of water 
on rock has an entirely different character. 
Tides or currents driven powerfully and con¬ 
stantly against a rocky shore, and bringing 
with them hard materials, may produce blunt, 
smooth surfaces, such as the repeated blows 
of a hammer on stone would cause; but they 
never bring it to a high polish, because the 
grinding materials are not held steadily down 
in firm permanent contact with the rocky 
surfaces against which they move, as is the 
case with the glacier. On the contrary, be¬ 
ing dashed to and fro, they strike and re¬ 
bound, making a succession of blows, and 
never a continuous, uninterrupted pressure and 
friction. The same is true of all the marks 
made on rocky shores against which loose ma¬ 
terials are driven by water-currents. They are 
separate, disconnected, fragmentary; whereas 
the lines drawn by the hard materials set in 
the glacier, whether light and fine or strong 
and deep, are continuous, often unbroken for 
