370 Chamberlin and Salisbury — Relationship of 



The chemical changes in the sands and gravels are not con- 

 fined to their surfaces. Beneath the surface, and so far be- 

 neath as to be below the zone of active surface weathering, 

 there is evidence that great changes have taken place, denoting 

 the lapse of long intervals of time. The most obvious of these 

 changes is the extent to which the leaching and concentration 

 of coloring matter has been carried. Besides this there are 

 various other changes less clearly defined, but which in the 

 aggregate give to the whole series below the loess an appear- 

 ance of age which is unmistakable. The changes which the 

 Orange Sands have undergone since their deposition, certainly 

 appear to be several times as great as those which the loess has 

 suffered since its deposition. And while this might not be a 

 safe standard for chronological measurements, taken by itself, 

 it has a strong corroborative significance, since it falls into 

 correspondence with conclusions drawn from other lines of 

 evidence. 



Outside the drift region, the material underlying the loess 

 is often residuary earth derived from Paleozoic rock, instead 

 of from Orange Sand. So far as oxidation and the changes 

 induced by exposure are concerned, the residuary earths of the 

 Paleozoic rocks do not seem notably more affected than those of 

 the Orange Sands. This is but an eye estimate, and may be 

 erroneous quantitatively considered, though it is based on the 

 observation of hundreds and thousands of sections. But in any 

 case the fact of very profound affection of the pre-loessial sur- 

 face by atmospheric agencies in pre-loessial times, is believed 

 to be beyond dispute. And this is no isolated phenomenon. 

 Generally speaking, it holds throughout the length and breadth 

 of the extra-drift loess territory, within the limits of the 

 writers' observation, and by report much beyond. On this 



point Professor Hilgard writes :* "The Orange Sand as 



a rule contains nothing that is capable of further oxidation or 

 solution by atmospheric agencies, unless it be silex. Such com- 

 plete peroxidation and lixiviation, the effects of which have 

 been largely extended into underlying formations, unquestion- 

 ably indicates a long subaerial exposure, from which the north- 

 western stratified drift was in a great measure exempt." Dr. 

 Loughridgef likewise recognizes the presence of " a bed more 

 clayey and darker (than the loess) in color," between the loess 

 and Orange Sand at Hickman, Ky., and " 4 feet of the stiff 

 darker loam" below the loess and above the gravel at Columbus, 

 Kentucky. These " darker loams" represent the oxidized and 



* This Journal, vol. iv, page 266, 1872. The same point is repeatedly insisted 

 upon by Professor Hilgard in other articles in this Journal, and in his report on 

 the Agriculture and Geology of Mississippi. 



f Kentucky Geol. Surv., Jackson Purchase Region, F., 1888, page 78. 



