50 
THE PARALLEL ROADS OF 
suddenness of the transportation, allow no 
time for the abrasion which produces the 
smooth surfaces of water-worn pebbles or the 
polished and scratched surfaces of glacier-worn 
ones. In the latter case, we have seen that 
the pebbles, being so set in the ice as to 
expose only one side, may be only partially 
polished, while others, more loosely held and 
turning in their sockets, may receive the same 
high polish on every side. In such a case 
the lines will intersect one another, in conse¬ 
quence of the different position in which the 
stone has been held at different times. No 
such appearances exist in the water-worn peb¬ 
bles; their blunt surfaces, smoothed and 
rounded uniformly by the action of the water 
in which they have been rolled or tossed 
about, present everywhere the same aspect. 
The correlation between these different loose 
materials and the position in which they are 
found helps us also to detect their origin. 
The loose materials bearing glacier-marks are 
always found resting upon surfaces which have 
been worn, abraded, and engraved in the same 
manner, while the water-worn pebbles are 
everywhere found resting upon rocks the abra- 
