June 25, 1897]. 



SCIENCE. 



993 



DISCUSSION AND CORRESPONDENCE. 



IS THE LOESS OF EITHER LACUSTRINE OR SEMI- 

 MARINE ORIGIN? 



To THE Editor of Science : Mr. Hershey, in 

 your issue of Blay 14tli, urges anew the claims of 

 the lacustrine and submarine hypotheses for the 

 origin of that still problematic deposit, the loess. 

 The former has been considered for the last 

 forty or fifty years, and the barrier has not yet 

 been found to separate it from the sea. The 

 latter has been discussed for twenty-five years 

 or more, and uo trace of marine fossils have yet 

 been found to corroborate it, though if it were 

 true nothing would seem easier. 



The undersigned committed himself to the 

 lacustrine view in 1875 by naming a hypothet- 

 ical lake covering the loess of western Iowa and 

 Nebraska, Lake Missouri.* Even as late as 

 1891f he argued for a similar body of water for 

 the deposition of the extramorainic drift as well 

 as of the loess of the same region. But a study 

 of Lake Agassiz and of Lake Erie satisfied him 

 that the position was untenable. Perhaps the 

 strongest reason for changing his opinion was 

 the absence of all shore lines, like beaches or cut 

 slopes. These are a conspicuous feature in the 

 cases studied, but none have been found con- 

 nected with the loess. When we think how a 

 single storm builds a beach ridge sometimes on 

 the shores of lakes no larger than the one pos- 

 tulated ; when we remember, also, how little 

 eroded much of the plateau of northern Mis- 

 souri seems to be, we can accept neither his sup- 

 positions that they may have been entirely re- 

 moved by erosion, nor the still more improbable 

 one that no beaches were formed, ' ' because the 

 shore line did not remain at one level a sufii- 

 cient length of time." In his appeal to western 

 Florida as an instance of the latter case he ad- 

 mits that the surface is 'undulating,' which 

 rouses the suspicion that a more comprehensive 

 study of it would prove that character to be the 

 result of beaches much eroded, though probably 

 modified by dune action, and possibly by solu- 

 tion of the underlying rock. 



He refers to a deposit which he has observed 



*Proc. A. A. A. S.,1875. 



tProc. Iowa Acad. Sci., 1891, p. 5, and Am. Geol., 

 1892. 



1,000 feet A. T. between Cuba and Pacific City, 

 Mo., as closely resembling the 'upland loess' 

 of northwestern Illinois. Before we admit the 

 extension of a loess-depositing gulf to that alti- 

 tude — for such a body of water as would cover 

 that and the clayey loam of Illinois could not 

 have been separated from the ocean — let us con- 

 sider some of the things involved in such a 

 view. It involves the submergence of St. Louis 

 500-600 feet, of northern Illinois nearly the 

 same, unless there was an elevation in that di- 

 rection instead of a greater depression, as has 

 been more commonly argued. It implies strong 

 wave action, especially around the Ozark uplift. 

 It implies remarkably discriminating erosion to 

 have removed so completely the loess and drift 

 from the nooks of that irregular shore, when it 

 failed to do so from the slopes and summits al- 

 most overhanging the gorge of the Missouri in 

 Boone county, Mo., or that of the Mississippi, in 

 Pike county. 



Before entertaining so violent a supposition, 

 why not refer the Cuba deposit to some local 

 lake, such as may be found in any residuary 

 area, or to an 'adobe' formation, or to ' a3olian 

 loess,' which no doubt accumulates in many lo- 

 calities to moderate thicknesses. 



Moreover, the gulf theory demands that the 

 sea submerged points, 1900-2000 A. T. in 

 northeastern Nebraska, and 1300-1400 in north- 

 eastern Iowa. And this, too, in regions which 

 shortly before and not long after had vigorous 

 streams flowing at considerably low-er levels. 



Against the fluvio-lacustrine or flooded river 

 theory for the Missouri ' upland loess ' Mr. 

 Hershey presents the objections, first, that it 

 was 'laid down on an undulated upland, dis- 

 sected by valleys,' and second, the 'inequali- 

 ties, when considered over broad areas, of the 

 surface of the sheet of loess or loam.' The 

 former must be more or less true in any super- 

 imposed drainage. And any alluvial plain is 

 far from even or level. The delta of the 

 Mississippi has a general slope toward the sea 

 of eight inches to the mile, with local slopes 

 for a few miles five times as great. The 

 fluctuations of water level have a range of 

 50 feet or more in some places. Moreover, 

 when we become acquainted with the habitual 

 creeping, or glacier-like, movement of clays and 



