THE NORMAL CURVE 53 



4401-4600. — Continued 



4571 perhaps represents a long and warm summer, since it 

 is thick at all localities measured. It is thickest 

 at locality 22, where it reaches 2}4 inches (6.5 

 cm.). 



4586-4634 at locality 20, see page 79 and Figure 16. 

 4601-4800. — Very good. The ice front stood far north of North- 

 ampton, and the sedimentation was very uniform. 



4618, 4633, 4661, 4742, and 4760 are certainly conspicuously 

 thick but may nevertheless represent warm sum- 

 mers. Numbers 4618, 4742, and 4760 are silty in 

 the Northampton region, and 4618 as well south 

 of Amherst. 



4654, at locality 19 only, represents an inconsiderable 

 drainage. It contains sand and is i}i inches 

 (3 cm.) thick. 

 4801-5000. — Very good. The different measurements show 

 excellent agreement. This is the case also with 

 the section at locality 18 which has mostly not been 

 used in calculating the normal curve, because the 

 varves are considerably thinner than those at the 

 other localities. 



4823 and 491 1 are silty but probably represent warm sum- 

 mers. 

 5001-5083. — Very good. Like the varves under 5000. 

 5084-5200. — -The agreement between the two curves (both 

 "11 Mass.," PI. II), is good considering the fact 

 that the upper curve is based on measurements of 

 the proximal parts of the varves and the lower one 

 on such of the distal parts. 



5176-5178, at locality 26, mark a drainage. They contain 

 fine sand and measure $}4, 2^4, and 2$4 inches 

 (13, 6.8, and 6.6 cm.) respectively. 



5184-5200, at locality 28, show very great variations in 

 thickness from year to year and therefore have 

 not been used in the normal curve. 



