NIAGARA 203 



is enclosed by higli and almost precipitous banks — covered, 

 at the time, with russet woods. A kind of mystery at- 

 taches itself to gyrating water, due perhaps to the fact 

 that we are to some extent ignorant of" the direction of 

 its force. It is said that, at certain points of the whirl- 

 pool, pine-trees are sucked down, to be ejected mysteri- 

 ously elsewhere. The water is of the brightest emerald- 

 green. The gorge through which it escapes is narrow, 

 and the motion of the river swift though silent. The 

 surface is steeply inclined, but it is perfectly unbroken. 

 There are no lateral waves, no ripples with their breaking 

 bubbles to raise a murmur; while the depth is here too great 

 to allow the inequality of the bed to ruffle the surface. 

 Nothing can be more beautiful than this sloping liquid 

 mirror formed by the Niagara in sliding from the whirlpool. 

 The green color is, I think, correctly accounted for 

 in the last Fragment. While crossing the Atlantic, in 

 1872-1873, I had frequent opportunities of testing the 

 explanation there given. Looked properly down upon, 

 there are portions of the ocean to which we should hardly 

 ascribe a trace of blue; at the most, a mere hint of indigo 

 reaches the eye. The water, indeed, is practically black, 

 and this is an indication both of its depth and of its free- 

 dom from mechanically suspended matter. In small thick- 

 nesses water is sensibly transparent to all kinds of light; 

 but, as the thickness increases, the rays of low refrangi- 

 bility are first absorbed, and after them the other rays. 

 "Where, therefore, the water is very deep and very pure, 

 all the colors are absorbed, and such water ought to ap- 

 pear black, as no light is sent from its interior to the eye. 

 The approximation of the Atlantic Ocean to this condition 

 is an indication of its extreme purity. 



