20 SMITHSONIAN" MISCELLANEOUS COLLECTIONS VOL. 5 1 



Maddren 1 makes the observation, "There is a little ice on top of 

 these bluffs, but nothing like the extensive development exposed in 

 the Old Crow Basin." Ice was also observed here by the writer, 

 which on first sight appeared to represent the typical ice-bed deposits 

 of many other localities. Upon closer examination, however, it was 

 found to be a superficial layer on the face of the exposure and not 

 a continuous ice-sheet interstratified with the muck and humus. 

 The formation of this layer of superficial ice appears to be of interest 

 and it may explain the presence of apparent ice-beds in some other 

 places. Moreover, it does show that caution should be exercised in 

 pronouncing all ice on the face of a cliff as being a section of a con- 

 tinuous bed. 



At (i) on the map (fig. 2), a deep depression or basin in the top 

 of the silt has been filled with alluvium and mucky material. The 

 brow of the escarpment here, three or four hundred feet back from 

 the edge of the stream, was estimated to be one hundred and fifty to 

 one hundred and seventy-five feet above the level of the river. The 

 Yukon, having cut laterally into the center of this basin, has left the 

 remaining muck resting on a slope of silt inclined toward the river 

 (see cross-section, fig. 3). By the undermining of the face of the 

 cliff, one block after another of this frozen muck has broken away 

 from its original position in the face of the escarpment and moved 

 riverward. In most instances this movement has been so gradual 

 that the blocks retain their upright positions and carry with them 

 the superincumbent turf and vegetation undisturbed. The thawing 

 of their faces and subsequent wasting away has allowed the turf to 

 bend down without breaking, thus affording protection against 

 further disintegration. The final destruction of the blocks, as they 

 eventually fall into the stream (where several were seen half sub- 

 merged), has resulted in leaving a basin-like area of an acre or more 

 in extent devoid of its former covering of from thirty to forty feet of 

 muck, except that here and there are masses recently detached from 

 the walls of the basin. The inclosing walls or faces of the basin are 

 perpendicular and from twenty to thirty feet in height. From three 

 to four feet below the top of the walls was a layer of ice. Upon first 

 sight it had every indication of being a section of a continuous bed. 

 Some of the detached blocks standing in the center of the basin 

 showed ice on both front and back faces. The top of this ice was 

 straight, but the lower margins were irregular when not covered by 

 the detritus at the foot. The face of the ice was also irregularly 

 melted, due to the more exposed position of some part<. 



'Maddren : Loe. cit, p. 18. 



