154 Scientific Intelligence. 



ous rising of the land to the north (as referred to in a notice of 

 his report in this Journal, vol. ix, p. 3 13); thus sustaining the 

 idea of an elevation of the interior of ' ' 

 of the Glacial period, and an elevatio 

 north. These conclusions— an elev 

 northward, followed after the Glacia 

 creasing northward — were reached v, 

 conceived hypothesis. 



Maud-bars.— Gen. Warren also describes with detail the form and 

 structure of the sand-bars in the Wisconsin River, giving facts that 

 are of general geological interest. The surface of these bars has 

 a gradual pitch up stream, and a steep front down stream — as in 

 a ripple mark. The sands are dropped where there is still water 

 along the shores, but the larger part in the still water on the 

 down-stream edge of the bars, thus building up this edge toward 

 the water's surface. The sand, where the current is strong, 

 " is moved along the gentle slope of the upper side till the crest is 

 reached, when it falls over and stops in the still water below." 

 The bar thus grows and becomes more convex in its down-stream 

 outline. Such sand-bars have a channel of deep water either 

 side, and also tend to make, by actum' as a dam at the low-water 

 stage of the stream, large areas of deep still water above them. 

 The changes in the current produced by the growth of the bars 

 and the greater changes from change of level in the river by 

 floods, produces frequent changes in the bars, so that they are not 

 the same in position from year to year. At very low water, the 

 bars may be mostly dry, with win is of water 



among them. This tends to improve the navigation for the time ; 

 but a rise, if small and temporary, sends the water across these 

 channels and fills them up. 



The sand-bars made in the Mississippi by the discharge of the 

 Wisconsin are of great extent. 1. 



channel to the west shore, they act as a dam and make an area of 

 relatively stiii water above, thus causing good navigation above 

 the junction and bad below — a common fact at junctions in the 

 rivers of the Mississippi basin. The Wisconsin River flows from 

 a region of much less summer rain than the .Mississippi, and is 

 often at low-water stage when the latter is high ; and hence it is 

 made very shoal by sand-bars formed in its mouth. 



The sands of the Wisconsin River bars are almo-i 

 ceous, and come from the drift deposits bordering its course. ' The 

 specific gravity, "excluding voids.'" of two specimens from dif- 

 ferent parts was 2-6392 and 26667. For comparison the specific 

 gravity of other sands was obtained, as follows: at St. 1'aul, 

 Minnesota, on the Mississippi, 2-6397; at Rock Island, lilim.i-, 

 ..fC'omie. ticui River, 2-6406; at 

 Block Island, R. L, 2-6392; at Newport, U. I., 26563. The 

 Report also compares different <a;ids ; !S to proportional fineness, 

 giving the proportion that passed through sieves of different 

 grades ; and, also, as to the changes in volume in different sands 



