288 Mr . T. A. Knight on ice found in the bottoms of rivers. 
were out of the water, and upon pieces of native rock, under 
similar circumstances, the ice beneath the water had acquired 
a firmer texture, but appeared from its whiteness, to have 
been first formed of congregated spicula, and to have subse- 
quently frozen into a firm mass, owing to the lower tempera- 
ture of the stone, or rock. Ice of this kind extended, in a 
few places, eighteen inches from the shore, and lay three or 
four inches below the level of the surface of the water, and 
did not dissolve nearly so rapidly as that which was deposited 
upon stones more distant from the shores. 
The cause of the appearance of large quantities of porous 
ice, in some of the continental rivers, upon a thaw taking 
place after a long and severe frost, may, I conceive, be ex- 
plained, without much difficulty, consistently with the fore- 
going hypothesis : for such ice would be removed by the 
increasing force of the rising water, and might be driven toge- 
ther in large masses, provided the temperature of the water 
were sufficiently low, and that it would be, if afforded by melting 
snow, or after having flowed over frozen ground. But there 
have been reports of large quantities of firm and solid ice 
having been found in this country at the bottom of deep and 
sluggish rivers, w here there existed neither streams nor eddies 
to occasion the descent of frozen spicula from the surface of 
the water ; and, if such ice have ever been found in such situ- 
ations, it must be admitted, that it could not possibly have 
been conveyed there by the means above-mentioned. 
I am, &c. &c. 
T. A. KNIGHT. 
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