350 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



looked from above upon the floating masses of ice, the whole mystery 

 would be solved. He would see that these masses were not formed at the 

 shore, and then detached, for they are nothing like shore ice. but were 

 formed on the bottom of the rapids; that they were ground-ice in fact, 

 and that be stood in the presence of one of nature's great ice making 

 machines. 



I shall now quote from notes of observations made during a series of 

 years, these notes being made on the spot, and they will go to show the 

 nature of the ground-ice which forms upon the rapids. 



Note 1st.— On the night of November 26th-27th, 1876, the mercury fell 

 to 0° F. for the lirst time this winter, and in the morning the floating ice 

 was running freely from the rapids, so as to fill the main channel of the 

 river, as far as the eye could reach. This ice, as seen from the i)ridge 

 above, consisted of quite large cakes, some with a smooth upper surface, 

 others again were rough, as if from having met some obstruction, there- 

 by breaking the upper crust, and forcing ttie fragments upwards along 

 the lines of fracture. As always observed before, beneath the upper 

 crust were projections, several feet deep, which seemed like great 

 sponges, as seen at the edge of the cake and through the transparent 

 upper crust, the adherent sand and gravel giving to some of these pro- 

 jections the almost exact appearance of stones. Their true nature is 

 however made quite manifest when the floating cake strikes the pier, the 

 apparent stone glides a short way up the slanting stone-work, and is evi- 

 dently of soft ice, like slushy and muddy snow. That these large cakes 

 are not of shore ice is evident from the fact, that the shore ice along the 

 rapids only formed last night, is only 20 or 30 feet wide, and is still ad- 

 herent as far as can be seen; besides, shore ice never has the muddy 

 masses like stones, nor the great irregular, projecting bodies, like 

 sppnges. 



Xote 2d.— March 4th, 1877. Mercury fell last night to 0° F. Same 

 appearances as above noted ; shore ice one inch thick and ten feet 

 wide. Upon returning to my oflice noticed the formation of ground-ice 

 on a miniature scale, in a small bottle of river water, left standing over 

 night on the window ledge ; here the water at the bottom of the bottle 

 being frozen by the cold external air coming up through the crevice be- 

 tween the sashes, would thus become lighter, would pick up the sand and 

 other sediment at the bottom, and rise with it to the top, here meeting 

 the warm air of the room it would melt and drop the sediment to the 

 bottom, to be again picked up and transported to the surface, and thus 

 the round went on. 



Note 3d.— February 11th, 1878. Mercury fell last night to 18° F. 

 Plenty of ground-ice running, simulacra of stones abundant. Shore 

 ice one inch thick and ten feet wide. 



Note 4th.— December 7th, 1878. This morning at 2 a. m. the first 

 ground-ice passed under the bridge, mercury then standing at 10° F., 

 being the first floating ice of the season. Shore ice one inch thick, and 

 about ten feet wide, just above the bridge. At 10 a. m. large cakes of 

 floating ice are passing by, with usual freight of sand, gravel, &c., sim- 

 ulating stones. 



