CLIMATE DURING RECESSION 93 



periods marked by moraines in 500 years, which gives the cycles 

 an average length of 55 years. This is exactly five sun-spot 

 cycles. At the present time no period of 55 years seems to be 

 known. If we assume that the nine periods represent 600 

 years instead of 500, the length of the cycles would be 67 

 years, that is to say two of Bruckner's 35-year periods. 

 Determination of the length of the period — i.e. the time of 

 recession and halt — by clay measurements would be of very 

 great value. In the clay graphs there are no particularly 

 thin varves which could be supposed to record these halts. 

 It would perhaps be hasty to conclude from this that the 

 pauses were due to increased ice supply rather than to lower 

 temperature and decreased melting. 



In Sauramo's (1918, PI. 3) diagram of the ice retreat in 

 southern Finland, based on a very detailed study, the fluctuations 

 of the rate are striking (Fig. 17). Leaving out of consideration 

 the part —650 to ±0, which represents the Fenno-Scandian 

 moraines, the Outer and, the Inner Salpausselka (cf. p. 87), the 

 ice edge halted or receded slowly on four occasions, at —1225, 



— 1050, —880, and —725. According to Sauramo's (1918, PI. 4) 

 graphs, the varves are practically normal during the years 



— 1225 to — 1221. They are uniformly thin during parts of the 

 halt —1085 to —1035, particularly during —1062 to — 1051. 

 The varves —900 to —872, i.e. those for the whole halt, are 

 especially at Sauramo's locality 19 thin and uniform. The 

 halt —725 is not distinguishable in the curves. This halt is 

 marked by a chain of transverse eskers (see Sauramo, 1918, 

 PL 1). The average length of the periods is 167 years, or five times 

 the Bruckner cycle. The facts seem to indicate that the halts 

 were primarily, but not exclusively, due to low temperature. 



The climate during the ice retreat also underwent changes 

 of longer amplitude. The length of the period recorded by the 

 readvances at Amherst and Claremont is about 1,700, and that 

 by those at Claremont and Inwood about 800 years. One-third 

 to one-fourth of the periods were occupied by readvances of the 

 ice edge. 



