OP THE PALLS OP ST. AtfTHONT. 887 



towards the east it forms the entire thickness of the drift, with the 

 exception of the surface-loam, or loess, the grey hardpan being 

 wanting. This is true of the general upland, while in the valley 

 of the Mississippi river the grey hardpan has been distributed 

 further east, reaching as far as St. Paul. The boulders in the 

 lower red hardpan are of many different kinds, but red quartzite 

 and trap of a green colour predominate ; while the upper or grey 

 deposit is distinguished by the presence of fragments of lignite and 

 Cretaceous debris, with large boulders of granite. Moreover the 

 stones in the red hardpan are generally smaller than those in the 

 grey. 



The lower bed has the bright red colour of peroxide of iron non- 

 hydrated, the colour of the upper being earthy, but becoming blue 

 at great depths. The iron in the latter is hydrated, or at least has 

 the usual characters and olive colours of limonitic earths, varying 

 from yellowish to reddish. The red boulder-clay is more gravelly 

 and sandy than the grey. It extends indefinitely eastward, and 

 was probably derived from the ferruginous shales of the Primordial 

 rocks, moved south-westwards by the great continental glacier 

 which preceded the latest glacial epoch. The grey deposit extends 

 indefinitely westward, forming the Leap Hills in Central Minnesota, 

 where it abounds in boulders and gravel, and the Coteau des Prairies 

 in Dakota, where it is sprinkled over with " alkali lakes." It 

 runs under the lacustrine clay of the Ked River of the North, and 

 it even there exhibits its strongly alkaline character by yielding 

 alkaline water when penetrated in deep wells. It is derived from 

 the disintegration of the Cretaceous shales and clays, which are 

 charged with sulphates of magnesia and lime and some bitter chlo- 

 rides ; and it often contains large pieces of that formation, even 

 within the limits of Hennepin County, in the state of Minnesota, 

 within which are situated the Palls of St. Anthony. This grey 

 hardpan represents the last cold epoch of the glacial period, and 

 was laid down by ice coming from the north-west and north. In 

 the state of Ohio, and in other places, the difference of colour in 

 the hardpan drift has been attributed to the downward infiltration 

 of the surface-waters to the depth of ten or twenty feet, causing a 

 hydration of the iron and perhaps of other earthy oxides ; but in 

 the vicinity of the Palls of St. Anthony this will not explain the 

 difference in colour of the upper and lower deposits. There is very 

 often between these two hardpan deposits a course of red sand, or 

 of red sand and gravel mingled with boulders, evidently the result 

 of a washing of the lower deposit and a stratification of its coarser 

 constituents by running water. Above this course of red gravel 

 and sand lies the grey hardpan, the colour changing immediately 

 from red to grey. It is not at all probable that if infiltrating water 

 changed the colour of the upper deposit, by hydrating the iron, the 

 process would cease so suddenly on reaching the underlying gravel 

 and sand. It would be more likely to have continued through the 

 gravel and sand, and ceased on reaching the impervious red hardpan 

 below. Besides, although the upper portion of the grey hardpan 



