THE ORIGIN OF GUMBOTIL 123 



by the colloidal clays, perhaps the kaolin contained in it, the color 

 of the colloidal material being sufficiently strong to mask the 

 reddish-yellow color of any oxidized iron which may be present. 

 This doubtless is responsible for the belief held by some persons 

 that the iron in the gumbotil is deoxidized or reduced, a condition 

 which could hardly be possible in the presence of the oxygenated 

 soil solution. 



The chemical analyses of the gumbotils from different drifts 

 and localities show, with respect to certain constituents, a striking 

 similarity. This is" especially true for the iron and sihca and, as 

 we might expect, for the calcium. Slight fluctuations may be 

 expected due to differences in the nature of the original rock materi- 

 als, to the amount of rainfall, or to leaching from above. It may 

 be concluded, therefore, that all gumbotils have a common origin — 

 the chemical modification by weathering of glacial till. 



Similarities of the gumbotils and the adjacent yellow oxidized and 

 leached zones.- — Furthermore, the chemical analyses, as arranged 

 in Table V, show a slightly less striking similarity between the 

 gumbotil and the yellow oxidized-leached clay. Naturally one 

 should expect to find a slightly greater concentration of the dif- 

 fusible material in the leached zone. One should expect also tO' 

 find a slight variation in the proportion of any one constituent 

 between the top and the bottom of any single zone. Each level 

 in any one zone is still slightly unleached with respect to another 

 level close to and above it. 



The proportions of most of the constituents present in the 

 oxidized-leached and gumbotil zones differ in most of the series 

 by only a few tenths of i per cent. When greater deviations occur 

 it can be shown that one or more of the upper strata have been 

 removed before the leaching process was completed. The dis- 

 tinguishing features between these two strata are, therefore, due 

 primarily to differences in the physical properties, and these 

 properties are chiefly the colloidal properties of the clay itself. 

 It is possible that two forms of the same material are being dealt 

 with, namely, the gumbotil, a highly colloidalized form, and the 

 oxidized-leached clay, the non-colloidalized form, that is, a form, 

 which in the presence of electrolytes is incapable of assuming. 



