318 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 



suggested correlation with the more prominent short-cycle varia- 

 tions of weather and solar radiation as noted by Clayton (1923). 



To form a " normal curve " for the entire series of varved clays at 

 Haverstraw, the five partial sections shown on Figure 2 and those 

 from other similar sheets were averaged and drawn as one curve to 

 form the Reeds graph represented in the lower portion of Figures 3 

 to 13. The Reeds curve is characterized by dark shading for the 

 winter layers. The Antevs Haverstraw curve, consisting of 732 

 varves, occupies the middle position, while the curve of the New 

 Haven sediments, representing 343 varves, is placed at the top. The 

 varves as represented in the three curves correlate closely. Each of 

 these curves represents the mean of the varve measurements taken 

 in different clay pits. They are thus " normal curves." Antevs' 

 curves have been developed from measurements taken in the field 

 usually from three to five sections, while the data for Reeds' curve 

 have been taken from field samples preserved in metal trays. The 

 normal number of parallel sections used by Reeds was 5, but in some 

 portions of his curve as many as 14 sections were averaged. 



When the Haverstraw and New Haven varved clay graphs are 

 compared they agree closely in contour. The mean, however, of the 

 Reeds Haverstraw curve shows an average thickness of 35 mm., the 

 Antevs Haverstraw curve 32.31 mm., and the Antevs New Haven 

 curve 23.24 mm. These graphs show, furthermore, a variation in 

 the thickness of sediments in groups of 3, 4, or 5 years, with occasional 

 larger and smaller groups. This group arrangement suggests a 

 correlation with the weather and solar radiation changes as noted by 

 Clayton (1923). Accordingly, the mean of each four consecutive 

 varves, in each curve, has been taken and set above the normal curve 

 by using the mean of each curve as a base line — that is, the 35 mm. 

 line in the Reeds curve. The consecutive groups of four varves, 

 which were averaged in this manner, have been joined by a horizontal 

 line near the base of each graph. The Reeds Haverstraw curve has 

 been further smoothed by taking the mean of each two consecutive 

 groups of four varves — that is, 8 varves, as indicated on the charts ; 

 also of every 11 varves. According to Clayton, the 8 or 11 year 

 curves give some idea as to what the sun-spot curve for this 736-year 

 period might have been like. 



These smoothed curves show not only the more prominent group 

 fluctuations in the deposition of the clay, but also those minor stages 

 in the melting of the retreating ice fields. When the curve is above 

 the mean, it indicates a period of more active melting and deposition 

 and the reverse conditions when it is below. 



In Figure 14 the smoothed curve, derived from Reeds' normal 

 curve by taking the mean of each successive group of four varves, 



