GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 173 



Rocks exposed to the action of breakers upon the sea coast, 

 'exhibit less of irregularity of surface than those at such a spot as 

 Bellows Falls, and especially are they usually wanting in what 

 are called pot holes. Nevertheless, they appear widely different 

 from those which have been subjected to glacio-aqueous agency. 

 The former rarely show any stria? ; or if occasionally produced 

 by bowlders, or ice, driven over the surface by powerful storms, 

 the marldngs are wanting in that parallelism which is so charac- 

 teristic of glacio-aqueous action. In short, although it was natural 

 before we were made acquainted with any other agent that could 

 produce the smoothing and striae of .rocks connected with drift, to 

 impute them to currents of water, yet a careful examination has 

 satisfied me, not only that they can almost always be distinguished 

 from the effects of running water and of breakers, but that they 

 are totally inexplicable by such causes ; although I doubt not that 

 currents of water have been concerned in their production. 



The remarkable parallelism of these striae is another fact inex- 

 plicable on the supposition that they were made by drift urged 

 over the surface by mere currents of water. Their direction in 

 different districts of country, does indeed differ many degrees. 

 But in a given district, the manner in which they retain their par- 

 allelism, over very irregular surfaces, is a striking peculiarity. 

 You will, indeed, sometimes see them turned aside a few degrees 

 where they pass over a very salient rock. But more commonly 

 they hold on their undeviating course, whether it carries them 

 directly towards the summit of a hill, or obliquely along its sloping 

 sides. Now it is most obviously impossible that matters driven 

 along promiscuously by currents of water, should produce such 

 effects. But suppose vast masses of ice, with bowlders frozen 

 into the bottom, to grate over the surface by expansion, or by 

 currents bearing them along, and this parallelism of the resulting 

 striae would be just what we should expect 



I have just alluded to striae existing on the sloping sides of 

 rocks ; and this point demands some further details. It has, 

 however, only of late attracted my particular attention ; and, 

 therefore, I cannot give as many facts concerning it as its im- 

 portance demands. As a general fact, it is only the northern and 



