374 THE EEGOLITH 



South of this limit ochreous-red and yellowish prevail. Along 

 the line of the Virginia railways south of Washington, these col- 

 ors prevail in hues of surprising brilliancy. Although the soils 

 throughout the region are residual, their colors seem quite inde- 

 pendent of the kind of rock to which they owe their origin. 

 Granite, gneiss, schist, or basic trappean rocks alike give rise to 

 red and yellow highly tenacious residues of such depth and bril- 

 liancy of color that every gully, ravine, and roadway stands out 

 against the green background of the landscape, as though painted 

 by some Titanic hand with brushes dipped only in yellow, red, 

 and vermilion ochres. These contrasts are particularly striking 

 in the early summer and directly after a rain. But he who 

 wishes to admire had best do so from his window, and without 

 too much attention to detail. 



The soil is plastic and adherent to an intolerable degree. The 

 grass forms no compact sod, as in the North, and as a result 

 the walls of houses, fences ; feet, legs and clothes of pedestrians 

 become stained a dirty ochreous color equally trying to the 

 housewife and to ploughman. 



The cause of this color variation has been the subject of 

 discussion by Professors Crosby,^ Dana,^ Russell,^ and others. 

 So far as our knowledge now extends, it is apparent, as first 

 stated by Crosby, that the difference is due to a spontaneous 

 dehydration which takes place in the warmer regions, whereby 

 the hydrous sesquioxides of the type of limonite and gothite 

 are converted into the less hydrated or anhydrous forms tur- 

 gite and hematite with corresponding changes in color from 

 yellow or brown to red. 



This view is rendered the more plausible from the fact that 

 the most brilliant hues are quite superficial, and below the sur- 

 face, fade out gradually into brown and yellow or even gray hues. 

 Such a transition may be observed in any fresh road cut, but 

 quickly become obscured by the washing down of the deeply 

 colored material from the higher levels. Sometimes the brilliant 

 red will be found a mere wash, but a fraction of an inch in 

 thickness, or again it penetrates to the depth of a foot or more 

 before giving way to more modest hues. In such eases the 



^ Proe. Boston Society of Natural History, 1885, p. 219, and Technological 

 Quarterly, Vol. lY, 1891, p. 36. 

 ''Am. Jour, of Science, Vol. XXXIX, 1890, pp. 317-319. 

 «Bull, No. 52, U. S. Geol. Survey, 1889. 



