Januakt 15, 1915] 



SCIENCE 



105 



belief tliat the loess of the region under con- 

 sideration is of fluviatile and not of eolian 

 origin,"^ and " the submergence during the 

 deposition of the loess."* 



However, changing the figure, there is rea- 

 son for suspecting that some have secret long- 

 ings for a geological statute of limitations 

 which would remove responsibility for state- 

 ments expressed a few years ago. 



Fortunately for the sake of long and inter- 

 esting debate, it seems impossible to say the 

 last word on the origin of the loess. Never- 

 theless, some, perhaps weary of the contro- 

 versy, or perhaps for novelty, have seemed 

 ready to compromise and admit that some 

 loess may have had one origin and some an- 

 other. Such an interpretation was placed on 

 the loess of southwestern Indiana in the re- 

 ports just referred to, and the principal object 

 of the present communication is to suggest that 

 another view concerning this material may be 

 tenable.^ The suggestion is perhaps somewhat 

 tardy, but it has received several years of 

 careful consideration. 



The correct interpretation of loess like that 

 of other geologic phenomena depends much 

 on the study of extensive areas. The writer's 

 first-hand knowledge of the loess comes from 

 most of the area of its occurrence in the 

 United States from Nebraska to Ohio, and 

 from Minnesota to Louisiana and also from 

 a part of that in Europe, but it has been par- 

 ticularly in the survey of the Quaternary geol- 

 ogy and physiography of a dozen quadrangles 

 in southern Illinois that he has been impressed 

 with the idea that the conclusions set forth 

 with regard to the loess of the Patoka quad- 

 rangle are not widely applicable. Naturally, 

 the attempt was made to correlate the work 

 in Illinois with that done in nearby districts, 



3 Water Supply paper No. 164 U. S. Geol. Sur- 

 vey, p. 46. 



^ ' ' The Physiographic Development of the Low- 

 lands of Southeast Missouri," p. 30. 



5 The loess is not the only surfieial material of 

 the Patoka quadrangle concerning which the 

 writer is inclined to a different view from that set 

 forth in the folio, but it is perhaps the most im- 

 portant. 



and for this purpose the Patoka area has been 

 visited a half dozen times in as many difier- 

 ent years. The object of the later visits was 

 to review the work done in previous years and 

 to make sure that none of the critical places 

 had been missed, though a complete survey was 

 not undertaken. 



Some quotations from the Patoka folio wiU 

 indicate the view there set forth. 



Previous to the present survey of the region no 

 attempt had been made to differentiate the sUta, 

 but evidence is now at hand for separating them 

 into two types: (1) thick, yellowish, calcareous, 

 and frequently stratified silts along the immediate 

 borders of the Wabash Valley, which are desig- 

 nated marl-loess, and (2) the more clayey, oxi- 

 dized and structureless silts designated as com- 

 mon loess, forming the general mantle over the 

 surface more remote from the river. The first is 

 believed to be of aqueous and the second of eolian 

 derivation. 



The marl-loess 



occurs at all altitudes from the flood plain to the 

 500-foot level (120 feet above the river), at which 

 altitude it frequently forms broad terraces and 

 flats . . . burying a rugged rock or till topography. 

 The thickness of the marl-loess in these terraces 

 and flats is sometimes 40 feet or more, but thick- 

 nesses of 10 to 200 feet are more common. 



The marl-loess is characterized by a high cal- 

 careous content and frequently by a sandy texture. 

 Calcareous concretions are exceedingly abundant. 

 In many instances it is delicately stratified and in 

 some cases is interbedded with sands or fine 

 gravels, or even carries scattering pebbles itself. 



The perfection of their stratification, their in- 

 terbedding with sand and gravel, the presence of 

 pebbles in them, their terraced form, and their 

 limitations to the borders of the Wabash point to 

 water as the most probable agent in the accumu- 

 lation of the marl-loess deposits, the deposition 

 probably being in a fluvio-lacustrine body occupy- 

 ing the lower Wabash Valley, into which the 

 silt was brought from- the lowan ice sheet by the 

 Wabash Eiver. 



The view expressed in the Bulletin of the 

 Geological Society of America, however, seems, 

 to be that the " marl-loess " is partly eolian 

 and the " common-loess " partly aqueous. To 

 the present writer it does not appear likely 

 that any of the loess of southwestern Indiana 



