C. ~R. Keyes — Eolian Origin of Loess. 303 



tubules. They are sometimes lime ; sometimes iron. The 

 origin of the latter appears to have been overlooked. As the 

 plant roots begin to decay they accumulate around them crys- 

 talline coatings of iron pyrites, which finally form little pipes 

 one-eighth to one-fourth of an inch or more in diameter, and 

 several inches long. The pyrites soon changes to limonite. 

 Along the Missouri River, all stages of tubule formation are 

 readily made out — from the decaying rootlet, with a thin film 

 of pyrites on it, though the crystalline aggregate of pyrites, 

 to the pyrite-limonite cylinder. Around all of the roots pyrites 

 does not form. Whether or not the pyrites is deposited on the 

 roots of a particular plant is not known. The fact that the 

 tubules are very abundant in certain spots and sparingly dis- 

 tributed or absent altogether in others suggests that the nature 

 of the plant has something to do with their occurrence. 



As a possible means of discrimination between water-laid 

 and wind-formed loess the tubules may prove an important 

 criterion. Should they occur at all levels in a deposit, the 

 indication would be that it had accumulated among plant 

 growths ; whereas if they are found only at the top, it would 

 be suggested tfoat the vegetation did not cover successively 

 every layer of loess, but only, as at present, the upper part. 



The chemical process of the accumulation of the iron pyrites 

 around the decayed roots of the plants in the loess is doubtless 

 analogous to the formation of the principal sulphide ores of 

 lead, zinc and iron in the same region of south Missouri. It is 

 a comparatively rapid process under favorable circumstances, 

 different rates of deposition prevailing with the different ores. A 

 decade or even less is probably ample time for the accumulation 

 of iron pyrites to a thickness of a quarter of an inch. The 

 process is in all likelihood in operation at the present time and 

 the deposition of pyrites in tubules, as well as the zinc and 

 lead in the rock crevices, is going on to-day as rapidly as it has 

 ever gone on in the past. 



The fossils of the loess have never received the critical atten- 

 tion that they deserve. A careful consideration of them 

 promises very fruitful results. Their real significance and 

 possible usefulness as a means of discriminating between loess 

 deposits having different origins can only be merely alluded to 

 here. In proportion to the great amount of study that the 

 loess has received from many individuals, it is a rather remark- 

 able fact that the fossils have received so little notice. What 

 little special consideration they have had is contradictory, and 

 is from a biological rather than from a geological standpoint. 

 R. E. Call and B. Shemik have both collected largely the loess 

 fossils ; but the conclusions reached are diametrically opposed. 

 The one argues that the organic remains when compared with 



