5QO PHYSICAL GEOGRAPHY. 



tilted up by elevating agencies like the Holyoke mountains. The fall- 

 ing of Niagara river over a precipice has worn out a narrow gorge seven 

 miles in length ; and the cataract is receding every year, and will con- 

 tinue to move backwards till Lake Erie is reached. Elsewhere the softer 

 rocks may determine the position of the eroding river. 



I have mentioned these cases because they are familiar, but take the 

 ground that every one of our hills and valleys has been moulded into 

 the particular shape for which its materials are fitted by the action of 

 the sculpturing agents. 



It is also true that rock-sculpture is largely dependent upon geograph- 

 ical position. The Egyptian traveller finds the chisel-work of fifty 

 centuries ago as plain as that made a year since upon a New England 

 sandstone. A dry climate is adapted to preserve, while one charged 

 with moisture and cold rapidly disintegrates nearly every known sub- 

 stance. Hence the same rocks, which are interminably channelled on 

 the eastern slopes of the Andes, are jagged and precipitous on the rain- 

 less western sides of the same range in Peru. No agent has been more 

 effective than ice in subduing the rougher elements of scenery ; and for 

 this reason the sublime and awe-inspiring elements are largely wanting 

 in our landscapes. The relentless glaciers have removed the pinnacles, 

 smoothed the northern slopes, and toned down our valleys, allowing the 

 picturesque feature to become predominant, and having regard, also, to 

 the agricultural necessities of the land. 



The understanding of the forces which have fashioned our topograph- 

 ical structure is complicated by the great length of time erosion has 

 been going on, and the diverse character of the agents. If our territory 

 constitutes some of the oldest dry land in the country, as is advocated in 

 a previous chapter, not only the rains and snows of historic time, and 

 the glaciers of the Drift period, but the rains, snows, and ocean waves of 

 all geological time have been at work upon our rocks, and accomplished 

 herculean tasks of excavating, grinding, and transporting. The result 

 has been naturally the obscuration of shapes which certain summits 

 would assume under normal circumstances. Furthermore, the precise 

 amount of action in each period is only partially known. Hence a com- 

 plete knowledge of the causes fashioning our landscapes is of difficult 

 attainment, and its full enunciation tedious. We must be excused, there- 



