288 ANNUAL REPORT SMITHSOMAN INSTITUTION, 195 



success by the Geological Survey and other organizations and individ- 

 uals (Black and Barksdale, 1949; Wallace, 1948; Woods et al., 1948; 

 Pryor, 1947). 



Emphasis is placed on the great need for expansion of long-term 

 applied and basic research projects as outlined by Jaillite (1947) and 

 referred to by Muller (1945) for a clearer understanding and evalua- 

 tion of the problems. 



Recognition and prediction. — Recognition and prediction of perma- 

 frost go hand in hand in a permafrost survey. If natural exposures 

 of permafrost are not available along cut banks of rivers, lakes, or 

 oceans, it is necessary to dig test pits or drill holes in places to obtain 

 undisturbed samples for laboratory tests and to determine the char- 

 acter of the permafrost. 



Surface features can be used with considerable degree of accuracy 

 to predict permafrost conditions if the origin of the surface forms are 

 clearly understood. Vegetation alone is not the solution, but it can be 

 used with other factors to provide data on surfic.al materials, surface 

 water, character and distribution of the permafrost, and particularly 

 on the depth of the active layer (Denny and Raup, unpublished manu- 

 script ; Stone, 1948 ; Muller, 1945 ; Taber, 1943a) . Cave-in or thermo- 

 karst lakes (pi. 8, fig. 1) , thaw sinks (Hopkins, 1949 ; Black and Barks- 

 dale, 1949; Wallace, 1948; Muller, 1945), and ground-ice mounds 

 (Sharp, 1942a) are particularly good indicators of fine-grained mate- 

 rials containing much ground ice. Polygonal ground can be used with 

 remarkable accuracy also if the type of polygonal ground and its origin 

 are clearly known. Numerous types of struhturhoden^ polygonal 

 ground, and related forms have been described and their origins dis- 

 cussed (Wittmann, 1950; Richmond, 1949; Cailleux, 1948; Washburn, 

 1947; Troll, 1944; Sharp, 1942b; Hogbom, 1914). The type of ice- 

 wedge polygon described by LefRngwell (1919) (pi. 4) can be de- 

 limited from others on the basis of surface expression. The author's 

 work in northern Alaska ( 1945 to present) reveals that the polygons go 

 through a cycle that can be described as youth, maturity, and old age — 

 from flat surface with cracks to low-centered polygons and, finally, to 

 high-centered polygons. Size and shape of polygons, widths and 

 depths of troughs or cracks, presence or absence of ridges adjacent to 

 the troughs, type of vegetation, and other factors all provide clues to 

 the size-grade of surficial materials and the amount of ice in the 

 ground. Frost mounds, frost blisters, icings, gullies, and many other 

 surficial features can be used with reliability if all factors are con- 

 sidered and are carefully weighed by the experienced observer. 



Geophysical methods of locating permafrost have given some prom- 

 ise (Sumgin and Petrovsky, 1947; Enenstein, 1947; Swartz and Shep- 

 ard, 1946; Muller, 1945; Joestings, 1941). (See p. 282.) Various 



