38 NEW YORK STATE MUSEUM 



land surface is however unknown, and the run-off of the surface 

 waters is ahvays concentrated along certain lowest lines, thus con- 

 stituting brooks, streams and rivers. While there may be numer- 

 ous drainage lines of this type, they generally unite intO' a few mas- 

 ter streams, the direction of whose flow is down the inclination 

 of the surface of the land. Such streams are known as consequent 

 streams, their direction of flow being consequent on the original 

 slope of the surface. 



When the strata of the Niagara region became a part of the dry 

 land, from the relative lowering of the water level (which may have 

 been due to rise of the land or to drawing off of water by the deepen- 

 ing of the oceanic basins), they formed a broad, essentially 

 monotonous belt of country fringing the old-land on the north, i. e. 

 a marginal coastal plain. The strata of this plain had a gentle 

 southward inclination, a feature shared by the surface of the plain. 

 Consequent streams quickly made their appearance on this plain, 

 a number of them probably coming into existence almost simul- 

 taneously and running essentially parallel from the old-land, across 

 the new coastal plain into the sea. These streams soon cut down 

 into the coastal plain, carving channels for themselves and thus es- 

 tablishing definite lines of drainage. As the streams at first con- 

 sisted entirely of the run-off of the moisture which fell on the plain 

 and in the higher old-land portion, it is evident that, unless the 

 rainfall was continuous, or unless extensive snow fields were present 

 to supply water, these young streams must have fluctuated greatly 

 in volume of.water, and at intervals become entirely dry. This con- 

 dition continued till the valleys, cut by these streams of run-off 

 water, had become sufficiently deep to reach the level of the under- 

 ground water, when the supply, augmented by springs, became 

 much more constant. Thus in course of time large valleys, supplied 

 with large rivers, came into existence. Meanwhile the sides of the 

 river valleys were attacked by the atmosphere, and degradation of 

 the cliffs cut by the stream resulted. 



As long as a river is narrow and vigorously undercuts its banks, 

 the latter will be steep, and the river channel will have the character 

 of a gorge. This generally continues as long as the river is cutting, 



