1 882.] The Loess of North America. 373 



ing purely local. So perfect is the homogeneity that very careful 

 examinations of specimens of soil from the Missouri valley, and 

 the valleys of the Des Moines and Iowa rivers, failed to reveal 

 even slightly marked physical differences. A peculiar feature of 

 the loess — in all parts of the world— is the presence of numerous 

 calcareous concretions— the locssmannclicn of the Rhenish deposits 

 — which occur in zones, at varying distances throughout the mass. 

 They assume allpossible shapes from the spherical (Plate v, Fig. 4) 

 through the spheroidal to the oblong ; in all cases they are more 

 or less numerously studded with roughened projections. No one 

 shape seems to obtain more than another, and not unfrequently 

 several are found cemented together/forming an eccentric single 

 mass. They are certainly characteristic of the loess, for that forma- 

 tion nowhere occurs without their presence. They are decidedly 

 hydraulic as would be naturally inferred from their constitution. 

 In no case have I ever observed fossils — either mollusks or vege- 

 table matters— acting as a nucleus. On one occasion, 2803 of these 

 bodies were crushed with that especial point in view. In nearly 

 every instance, 2789, they were found to contain loose fragments 

 broken by some means from their inner walls, but no foreign sub- 

 stance whatever could be detected. 1 In the remaining fourteen 

 specimens, while the concretions were hollow, they yet contained 

 loose particles of no substance whatever. Not a single specimen 

 was solid throughout. That they were 'originally solid, or of a 

 pasty consistency, is not to be doubted, as a study of the inner 

 surface reveals. They all present a deeply fissured interior (Plate 

 v, Fig. 1),- consequent on the evaporation of water and subse- 

 quent contraction. In the vast majority of cases the pyramidal 

 masses of the interior showed distinct irregularly concentric lines 

 of growth, or rather of accretion (Plate v, Fig. 2). The presence of 

 these zones and the peculiarly granulated surfaces of the crushed 

 masses, with entire absence of distinct crystallization when viewed 

 under the microscope 3 complicates somewhat the problem of their 



