NOTE ON THE ACTION OF FROST ON SOIL. 



The action of frost in altering the surface of the soil was well 

 shown during the period of cold weather which prevailed over 

 the Puget Sound region from February lo to i8, 1903. During 

 this time heavy white frosts formed every night, the temperature 

 falling as low as 24° Fahrenheit, and ice formed three inches 

 thick in open water. In the direct rays of the sun the surface 

 thawed daily, but in shaded places the melting that took place 

 was slight. The ground was not frozen at the beginning of the 

 period mentioned. 



The first night's frost had its usual effect of raising the sur- 

 face of loose ground, which was well illustrated in gravelly soil, 

 A layer of ice consisting of vertical prisms five-eighths of an inch 

 long formed during the night at a depth of about three-eighths of 

 an inch below the surface, thus raising the overlying material 

 without otherwise disturbing it. The cold of the following night 

 produced a similar layer of ice almost an inch thick below the 

 first one, raising the latter along with its load of sand and gravel. 

 A slight thaw took place on the day after the second cold night, 

 the second day of observation. Specimens taken from shady 

 spots early on the following day showed three layers of frost 

 (Figs. I and 2), of which the top one had melted down unevenly, 

 being almost destroyed in some places. The larger pebbles, 

 absorbing and radiating a great amount of heat during the day, 

 had settled through the ice to depths varying with their weight 

 and shape. 



After six nights the laminated structure presented the appear- 

 ance shown in Figs. 3 and 4. In some cases the line of division 

 between adjacent layers is difificult to locate in the figure, 

 although it could be found in the specimens. The fifth and sixth 

 nights were not quite so cold as those preceding, and it is to be 

 noted that they yielded crystals of shorter growth, about three- 

 eighths of an inch in length. By the eighth day all the layers 



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