Newberry — Geology along the Northern Pacific P.P. 337 



Harignac constructed a table of specific gravities of colum- 

 bite which showed that in general the specific gravity increases 

 with the amount of tantalum. The relations which he found 

 hold good for this analysis. 



Art. XLIY. — Notes on the Surface Geology of the country border- 

 ing, the Northern Pacific Railroad; by J. S. Newberry. 



From Chicago through Wisconsin and Minnesota the Northern 

 Pacific Eailroad passes over an almost unbroken sheet of drift, 

 which, though of great interest, has been so fully described in 

 the able reports of Messrs. Chamberlin, Winchell and Upham, 

 that nothing further need be said herein regard to it. 



Going west from Duluth to Brainerd the line of the road for 

 the most part lies in what is evidently the old deserted bed of 

 a westward extension of Lake Superior. The ground is still 

 low and swampy and much of the surface is formed of what is 

 unmistakably lake sand. 



At various points farther west true till is seen with its 

 striated pebbles ; and one such exposure at Audubon is within 

 reach of every traveler. Beyond this, bowlders scattered over 

 the surface and pebbles in the ditches continue as evidence 

 of the transport of material from the eastern highlands. About 

 Bismarck the bowlders though fewer are still not rare and are 

 gathered in groups and trails, as elsewhere along the margin of 

 the drift area, suggesting transport by ice floats. The last of 

 these bowlders is seen at Sims, about twenty miles from Bis- 

 marck. From this point to the crossing of the Little Missouri 

 one can hardly find a stone to throw at a bird or a shrub big 

 enough for a tooth pick. 'This is an extension northward of 

 that broad prairie area which I have crossed in many places 

 farther south. Here, between the eastern drift and that from 

 the Rocky Mountains, the soil is formed entirely by the decom- 

 position of the underlying rocks, and wherever these are shales 

 and calcareous sandstones, as they are throughout most of the 

 Cretaceous formation, there are no outcropping ledges of rock; 

 the country is smooth and stones of all kinds are scarce. This 

 belt, which runs from the Mexican to the Canadian line, is 

 prairie because of the dryness of the climate and not on account 

 of the soil or the geological substructure ; for between the 

 "Cross timbers " and the Raton Mountains with a considerable 

 variety of geology and topography, there are no trees except 

 along the water courses, which, fed by the melting of the snows 

 on the Rocky Mountains, are perennial and supply constantly 

 the amount of moisture that is a necessity for tree growth. 



