IV. 



having been removed by the stream. This process of gorge 

 cutting by natural agencies may be compared to artificial 

 trench cutting for laying water pipes, where the sides of the 

 trench commonly show the cut edges of the layers of sand, 

 gravel or rock, which before cutting, were continuous. The 

 tools with which nature cuts are: rock fragments, broken off 

 bv frost action, and carried by the stream over the bed-rock; 

 loose stones and sand which the current sweeps along, and 

 cakes of ice, which in early spring, float down stream. 

 The mode of cutting the natural trench differs from that 

 emploved in cutting the artificial trench, in that it consists 

 of a scraping, graving and pounding action, instead of a 

 digging and blasting action. The results are similar in 

 both cases, but the time occupied by nature in doing the 

 work is vastly longer than that occupied by man in cutting 

 a trench of similar magnitude hx his more improved 

 methods. But as nature has all eternity at her disposal, it 

 matters not how slow she works. 



While the trench is slowly deepened and widened, the 

 atmosphere attacks the cut sides and breaks up the exposed 

 portions of the strata. This is accomplished by the mechan- 

 ical activity of freezing water in the fissures and between the 

 layers, which are pried apart by the growing ice crystals, 

 as well as by the chemical activity of the atmospheric gases 

 and moisture, which cause the decomposition or decay of the 

 rock. Thus the sides are degraded from perpendicular naked 

 precipices to gently descending soil-covered slopes. The bed 

 of Lake Erie may be regarded as such a natural trench of 

 excessive width as compared with its depth. The opposite 

 side of this trench is formed by the cliffs of the Canadian 

 shore, though these, from the direction of the trench and the 

 dip of the strata, consist of a different kind of rock. The 

 New York bank of this trench is kept more or less fresh by 

 the continual cutting of the waves, which has gone on ever 

 since the waters of Lake Erie filled the trench and converted 

 it into a lake. 



