150 Minnesota Academy of Science 



evidence, along with the common stratification, that the sup- 

 posed soil is only a part of the common loess accidentally 

 given a darker color, cither by being more moist or by the dis- 

 tribution in the sedimentation of some coloring matter. In 

 the Carboniferous formation along that portion of the Missouri 

 bluffs is a considerable dark shale, so black and carbonaceous 

 that it has led locally to search for coal. To me the most 

 likely explanation of a dark sheet parallel with the stratifica- 

 tion of the loess at this place is the erosive action of the river, 

 or wash from its banks by some tributary stream, at the proper 

 time, upon this mass of Carboniferous shale. If it were an old 

 soil, it would show roots of old vegetation, and if they were 

 to be seen Professor Shimek would certainly have mentioned 

 them. But, admitting that this dark layer is actually an old 

 soil, it seems as reasonable to suppose that, in the valley of 

 the great river, it might be buried by water as by wind. 



Thirdly, Professor Shimek produces "additional convincing 

 evidence" from a comparison of the loess lying below the 

 "soil" layer with that above it. This lower loess is somewhat 

 discolored toward the top, "close-grained, easily cut through, 

 compact, yellow, with bluish-gray lines and streaks, especially 

 in its lower part, fossiliferous, with occasional iron tubules, 

 and showing the characteristic laminated structure when 

 broken vertically. Unlike the upper, disturbed, layer, it con- 

 tains few but larger and round nodules of calcium carbonate. 

 The shells are all terrestial and chiefly Succinea ovalis." Bar- 

 bour reported the finding of scattered fragments of bone in this 

 lowest loess, but Shimek found none. It is not difficult to see 

 that the points of difference between this and the upper 

 stratum are nothing more than could be seen anywhere in the 

 great loess sheet, and amount to nothing as evidence indicating 

 differences in origin or in structure or in date. 



It is, however, noteworthy that Professor Shimek took 

 notice of the horizontally laminated structure, and calls it 

 "characteristic" of the loess. It is necessary to say only that 

 there are other deposits which geologists find characteristically 

 stratified and laminated, namely, all the sedimentary rocks of 

 the earth's crust, amounting to several miles when they are 

 placed one on the other : limestones, sandstones, shale, coal, 



