408 LAKE SUPERIOR. 



parallelism with each other, but crossing another system, more or less 

 strongly marked, of other lines equally parallel with each other. At 

 other times, a system of lines, strongly marked and diverging very 

 slightly, seem to pass over another system, in which the lines form 

 various angles with each other. Again, there are places, and this 

 is the most common case, where the lines diverge slightly, following, 

 however, generally one main direction, which is crossed by fewer 

 lines, forming more open angles. These diiferences, no doubt, indi- 

 cate various oscillations m the movement of the mass which produced 

 the lines, and show probably its successive action, with more or less 

 i itensity, upon the same point at successive periods, in accordance 

 with the direction of the moving force at each interval. The same 

 variations within precisely the same limits may be noticed in our day 

 on the margin of the glaciers produced by the increase or diminution 

 of the bulk of their mass, and the changes in the rate of their move- 

 ment. 



The loose materials which produced, in their onward movement 

 tinder the pressure f ce, such polishing and grooving, consisted of 

 various sized boulders, pebbles and gravels, down to the most minute 

 sand and loamy powder. Accumulations of such materials are found 

 everywhere upon these smooth surfaces, and in their arrangement 

 they present everywhere the most striking contrast when compared 

 with deposits accumulated under the agency of water. Indeed, we 

 nowhere find this glacial drift regularly stratified, being everywhere 

 irregular accumulations of loose materials, scattered at random with- 

 out selection, the coarsest and most minute particles being piled 

 irregularly in larger or smaller heaps, the greatest boulders standing 

 sometimes uppermost, or in ths centre, or in any position among 

 smaller pebbles and impalpable powder. 



And these materials themselves are scratched, polished and fur- 

 rowed, and the scratches and furrows are rectilinear as upon the 

 rocks in situ underneath, not bruised simply, as the loose materials 

 carried onward by currents or driven against the shores by the tides, 

 but regularly scratched, as fragments of hard materials would be if 

 they had been fastened during their friction against each other, just 

 as we observe them upon the lower surface of glaciers where all the 

 loose materials set in ice, as stones in their setting, are pressed and 



