RECORDS MADE BY RIVER ICE. 11 ( .) 



Gravel Heaps deposited by Elver Ice. — On the low, sandy shores of the 

 Yukon, especially on the up-stream ends of low islands, there are frequently 

 heaps and ridges of gravel accumulated by the ice. The simplest of these 

 deposits are heaps of rounded, water-worn stones and bowlders, resting on a 

 sand flat. They are of all sizes up to those containing two cart-loads or more 

 of material. Down-stream from those heaps which occur below high-water 

 mark, there is frequently a trail of fine sand, tapering to a point some fifteen 

 or twenty feet distant, showing that water has flowed over them and deposited 

 sand in the eddy below. 



In other instances, also quite common on low, sandy shores, the gravel 

 was arranged in ridges a few inches high, which intersected and crossed one 

 another so as to enclose bare, slightly basin-shaped spaces, from a few inches 

 to several feet in diameter. Sometimes these ridges of gravel bore a fanciful 

 resemblance to letters, as if some one had tried to write an inscription on 

 the sand by piling up lines of gravel. Again they were more regular, and 

 enclosed depressed areas that looked not unlike gigantic tadpole nests. 

 These resemblances, however, are mere fancies. 



The explanation of the presence of the ridges and of the gravel heaps is 

 to be found in the action of ice on the river banks during high water: The 

 ice adheres to the bottom of the river in many places during the winter and 

 is floated away in large cakes when the spring freshets come. The bottoms 

 of the cakes are charged with gravel, and when they run aground on low 

 shores, as often happens, and are melted, their load of stones is left behind. 

 In the heaps of ice formed on the shore the blocks are frequently turned on 

 edge, and on melting in that position leave the low ridges of gravel described 

 above. 



When low, sandy shores are covered with cakes of ice, leaving cracks 

 between, the gravel transported in the manner described finds lodgment in 

 the cracks, and when the ice melts forms ridges, some of which intersect and 

 enclose bare, sandy spaces. 



Pebbles Faceted, Polished, and Scratched by River Ice. — The most interest- 

 ing records made by river ice in Alaska occur on pebbles that are set in a 

 matrix of tenacious clay, and form a pavement along the river banks. A 

 typical instance of this nature was observed on Porcupine river about one 

 hundred miles above its mouth. At this locality the steep bluff overlooking 

 the river is formed of tenacious blue clay and capped by a layer of water- 

 worn pebbles of various kinds and sizes. The pebbles on falling to the river 

 beach become imbedded in clay so as to form a veritable pavement along 

 the river over a space about one hundred feet broad during low water and 

 more than a mile in length. The upper surfaces of the pebbles set in the 

 clay have been ground down or faceted. The surfaces of the facets arc 

 smooth and crossed by striations which are in general parallel with the 



