COMPOSITION OF MARL-LOESS 



159 



in the range of the CaCOj constituent. The average sample of the com- 

 mon loess would probably show less than 1 per cent of the CaCOg, while 

 the average sample of the marl-loess would probably show more than 5 

 per cent. 



• Analyses of Loess and Marl-loess 



Constituent. 



Number 1. 



Number 2. 



SiOa 





71.20 



18.56 



1.34 



.15 



.14 





ALOo 





I 60.00 



Fe„Oo 





FeO 



.80 



CaO 





20.27 



CO2 





15.93 



TiOa 



.88 

 .52 



1.26 

 .32 



6.30 





MgO 





Na^O 



j- 1.00 



K2O 





HoO 



2.00 









Total 



100.67 



100.00 







Under the microscope, in addition to the quartz and comminuted 

 shell particles, grains of magnetite, mica, etcetera, may also be recognized. 

 In addition to the exceedingly fine sand mentioned, there are sometimes 

 present thin layers of medium or even coarse sand, and in a few instances 

 layers of pebbles were seen. Such layers do not appear to be confined 

 to any particular horizon of the marl-loess, fine pebbles and sand having 

 been found both at the base (southeast i section 9, township 4 south, 

 range 13 west) and at the upper limits (west J section 17, township 1 

 south, range 10 west) of the deposits. The lowest exposures are rather 

 more frequently of the gray clay type than of the coarser yellowish 

 variety, but the gray clays have, however, been noted up to the maxi- 

 mum altitude attained by the marl-loess — (500 feet above tide). 



Stratification. — Stratification is manifested by (1) a lamination of the 

 fine silts due to probable variation in composition as brought out by 

 color, (2) by the lamination of the same class of silts due to slight diff'er- 

 ences in texture, (3) by alternations of clay-like laminae with sandy 

 layers or of thicker clay layers with sandy beds, (4) by the presence of 

 layers of gravel, (5) by the horizontal linear arrangement of calcareous 

 concretions, and (6) by the similar horizontal character of the fossilif- 

 erous bands. 



The visible stratification is confined to the yellowish type, though the 

 well records and exposures appear to indicate that the gray t3^pe has an 

 approximately horizontal upper surface. The dip of the laminae when 



