278 



ANNUAL REPORT SMITHSONUAN INSTITUTION, 195 



caprice of mankind. For example perennially frozen mammals, 

 rodents, bacteria, artifacts, beds of sand and silt, lenses of ice, beds 

 of peat, and varied junk piles, such as kitchen-middens, mine dumps, 

 and ships' refuse heaps are individual items that collectively can be 

 lumped under the term permafrost. 



Ground perennially below freezing but containing no ice has been 

 called "dry permafrost" (Muller, 1945). 



-10 -5 



Degrees Centigrade 

 5-5 5-5 



Northern Alaska. 

 From well 25 miles 

 southwest of Barrow. _ 

 After J.H. Swartz 

 and G R. McCarthy 

 (written communication) 



Barrow, Alaska 

 (R.F. Black) 



500 



Yakutsk, U.S.S.R. 

 » \ After 



\ M.F. Sumgin, 1940; 

 \ Courtesy I.V. Poire' 



N 



r. 



Nome, 

 Alaska. 

 After 

 Taber 

 (1943a) 



Bukachacha, U.S.S.R. 



After 



D.V. Redozubov, 1946; 



Courtesy I.V. Poire' 



(a) 



(b) 



(c) 



FiQUBE 3. — ( a ) Representative temperature protiles in areas of continuous perma- 

 frost. (&) Representative temperature profiles in areas of discontinuous 

 permafrost. (c) Hypothetical temperature profiles in areas of sporadic 

 permafrost. 



Permafrost composed largely of ice is abundant particularly in 

 poorly drained fine-grained materials (pis. 1, 2, and 3). The ice oc- 

 curs as thin films, grains, fillings, veinlets, large horizontal sheets, 

 large vertical wedge-shaped masses, and irregular masses of all sizes. 

 Many masses of clear ice are arranged in geometric patterns near the 

 surface, that is, polygonal ground (pi. 4) and honeycomb structure. 

 The ice may be clear, colorless, yellow, or brown. In many places 

 it contains numerous oriented or unoriented air bubbles (pi. 5, fig. 1), 

 and silt, clay, or organic materials. Size, shape, and orientation of 

 the ice crystals differ widely (pi. 5, fig. 2). Discordant structures 

 in sediments around large masses of ice are evidences of growth 

 (Taber, 1943a; Leffingwell, 1919). 



Relation to terrain features. — In the continuous zone of permafrost 

 the upper limit (permafrost table, Muller, 1945) is generally within 

 a few inches to 2 feet of the surface. Large lakes and a few large 

 rivers lie in thawed areas slightly larger than the basins they occupy 



