226 GLACIAL GEOLOGY. 



to the opinion that loess is for the most part of aqueous origin. In 

 many cases this can be demonstrated, as by the occurrence of bedding 

 and the intercalation of layers of stones, sand, gravel, etc., in the de- 

 posit; again, by the not infrequent appearance of freshwater shells; 

 but perhaps chiefly by the remarkable uniformity of character which 

 the loess displays. It seemed to me reasonable also to believe that the 

 flood waters of glacial times must needs have been charged with finely 

 divided sediment, and that such sediment would be spread over wide 

 regions in the low grounds — in the slack waters of the great rivers and 

 in the innumerable tem])orary lakes which occupied or partly occupied 

 many of the valleys and depressions of the land. There are different 

 kinds of loess or loess-like deposits, however, and all need not have been 

 formed in the same way. Probably some may have been derived, as 

 Wahnscbaffe has suggested, from the denudation of bowlder clay. Pos- 

 sibly, also, some loess may owe its origin to the action of rain upon the 

 stony clays, producing what we in this country would call " rain- wash." 

 There are other accumulations, however, which no aqueous theory will 

 satisfactorily explain. Under this category comes much of the so- 

 called Berglms, with its abundant land shells and its generally unstrat- 

 ified character. It seems likely that such loess is simply the result of 

 sub aerial action, and owes its origin to rain, frost, and wind acting 

 upon the superficial formations and re-arranging their finer-grained con- 

 stituents. And it is quite possible that the upper portion of much of 

 the loess of the lower grounds may have been re- worked in the same way. 

 But I confess I can not yet find in the facts adduced by German geo- 

 logists any evidence of a dry-as-dust epoch having obtained in Europe 

 during any stage of the Pleistocene period. It is obvious, however, 

 tliat after the flood waters had disappeared from the low grounds of 

 the continent sub-aerial action would come into play over the wide 

 regions covered by glacial and fluvio-glacial deposits. Thus, in the 

 course of time these deposits would become modified, just as similar 

 accumulations in these islands have been top-dressed, as it were, and to 

 some extent even re-arranged. 



I am strengthened in these views by the conclusion arrived at by M. 

 Falsan, the eminent French glacialist. Covering the plateaux of the 

 Dombs, and widely spread throughout the valleys of the Ithone, the Ain, 

 the Isere, etc., in France, there is a deposit of loess, he says, which has 

 been derived from the washing of the ancient moraines. At the foot of 

 the Alps, where black schists are largely developed, the loess is dark 

 gray ; but west of the secondary chain the same dei)Osit is yellowish and 

 composed almost entirely of silicious materials, with only a very little 

 carbonate of lime. This Union, or loess, however, is very generally modi- 

 fied towards the top by the chemical action of rain, the yellow loess 

 acquiring a red color. Sometimes it is crowded Mith calcareous con- 

 cretions; at other times it has been deprived of its calcareous element 

 and converted into a kind of pulverulent silica or quartz. This, the true 



