94 PHYSICAL GEOGKAPHY. 



boulders we found there with their sides also flattened and 

 scored by the contact, resting upon the surface of the 

 quartzite; thus, as far it was possible, we detected them in 

 the very act of producing the effects we have described. This 

 scoring and chipping of the rocks in place is regarded as not 

 only satisfactory evidence of glacial action, but also of the 

 southerly movement of the glaciers. 



Direction of Glacial Currents. Speaking in general terms we 

 say that the movement of the glaciers was from north to south; 

 but the distribution of the boulders which were derived from 

 any particular northern point or region, shows that the current 

 or currents in which they were transported varied from a true 

 north and south line. So also we find the direction of the 

 striae or scratches which the glaciers have produced to have 

 been various, and considering that the country is, and has 

 always been without strongly marked surface-features that 

 would have necessarily deflected the ice-currents, the great 

 variation from a south line in the direction of some of the 

 striae is quite remarkable. 



The direction of the striae observed upon the Burlington 

 limestone, near Burlington several years ago, was found to be 

 south,* about twenty -two degrees east.f The locality in Mills 

 county, described in another part of this report, is upon 

 section 16, township 71, range 43 west, being upon the borders 

 of the valley of the Missouri river and about twenty miles 

 below Council Bluffs. Here there are two distinct sets of 

 scratches upon the same surface and crossing each other, 

 showing that the current was changed while the glacier was 

 moving over it, or that one of two neighboring currents over- 

 powered and displaced the other. One set has a direction 

 south, twenty degrees east, and the other, south, fifty-one 

 degrees east. The striae of both sets were found to be, as is 



* As we have such unmistakable evidence that the glaciers moved from the north, we 

 always take the most southerly eud of the strise to indicate the direction in which the 

 glacial current was moving at that particular place. 



t No allowance is made in any of these cases for the variation ol the magnetic 

 needle, which the local surveyors in the Missouri valley estimated at 11° east of north. 



