174 Scientific Intelligence — Hydrography. 



running off for a few hours into the Gulf Stream to thaw and get 

 warm, as she now does, she used to put off for Charleston or the 

 West Indies, and there remained till the return of spring before 

 making another attempt. A beautiful instance this of the import- 

 ance and bearings of a single fact, elicited by science from the works 

 of nature. — Annual of Scientific Discovery , p. 160. 



6, On the Falls of Niagara. — If we follow the chasm cut by the 

 Niagara river, down to Lake Ontario, we have a succession of strata 

 coming to the surface of various character and formation. These 

 strata dip south-west or towards the Falls, so that, in their progress 

 to their present position, the Falls have had a bed of very various 

 consistency. Some of these strata, as the shales and medina sand- 

 stone, are very soft, and, when they formed the edge of the Fall, it pro- 

 bably had the character of rapids ; but, wherever it comes to an edge 

 of hard rock, with softer rock-beds below, the softer beds, crumbling 

 away, leave a shelf projecting above, and then the fall is perpendi- 

 cular. Such is the case at present ; the hard Niagara limestone 

 overhangs in tables the soft shales underneath, which at last are 

 worn away to such an extent as to undermine the superincumbent 

 rocks. Such was also the case at Queenston, where the Clinton 

 group formed the edge, with the medina sandstone below. This 

 process has continued from the time when the Niagara fell directly 

 into Lake Ontario to the present time, and will continue so long as 

 there are soft beds underneath hard ones ; but, from the inclination 

 of the strata, this will not always be the case. A time will come 

 when the rock below will also be hard. Then, probably, the Falls 

 will be nearly stationary, and may lose much of their beauty from 

 the wearing away of the edge rendering it an inclined plane. I do 

 not think the waters of Lake Erie will ever fall into Lake Ontario 

 without any intermediate cascade. The Niagara shales are so ex- 

 tensive that possibly, at some future time, the river below the cas- 

 cade may be enlarged into a lake, and thus the force of the falling 

 water diminished ; but the whole process is so slow, that no accurate 

 calculations can be made. The Falls were probably larger, and 

 stationary for a longer time at the '' Whirlpool" than anywhere else. 

 At that point there was no division of the cataract, but at the 

 ** DeviFs Hole" there are indications of a lateral fall, probably 

 similar to what is now called the American Fall. At the Whirl- 

 pool, the rocks are still united beneath the water, shewing that they 

 were once continuous above its surface also.* — Agassiz on Lake 

 Superior, p. 15. 



6. On the Existence of Manganese in Water. — At a meeting of 

 the American Academy, in January 1849, Dr Charles T. Jackson 



* The data on which these and the previous remarks on the geology of the 

 Falls are founded, are derived from Professor James Hall's investigations in 

 the New York State Survey. A. 



