26 McGee — Southern Extension of Appomattox Formation. 



quarter of an inch in diameter sparsely disseminated through 

 the sandy layers ; third, in the exceptionally regular stratifica- 

 tion ; and fowrth, in the absence of the distinctive clay-out- 

 lined cross stratification — though the sandy strata are some- 

 times cross bedded. The formation here is exceptionally 

 ferruginous. A thin layer in a cutting three-quarters of a mile 

 east of Grand Bay is locally used as an ochre ; the plowed 

 fields and other exposed surfaces are sometimes besprinkled or 

 even shingled with small ferruginous nodules (or " buckshot ") 

 weathered out of the loam ; the prevailing colors are harsher 

 and generally darker than usual (though not so dark as at 

 Columbia), ranging from orange-yellow mixed with gray in 

 some strata, to prevailing orange-reds weathering to brick-reds 

 and chocolate-browns ; and the peculiar mottling characteristic 

 of the deposit under certain conditions of exposure through- 

 out nearly its whole extent is beautifully displayed. In the 

 railway section in the eastern part of Grand Bay the relation 

 between the mottling below the reach of ready oxidation and 

 the formation of the ferruginous concretions found on the sur- 

 face are clearly shown : the lower part of the exposure, 

 extending to within 10 or 12 feet of the surface, is of 

 fairly uniform orange or orange-yellow hue, with some strata 

 passing into gray ; next follows a stratum of 5 or 6 feet, con- 

 centric with the surface and discordant with the stratification, 

 in which the uniform hues are shot with vertical or oblique 

 lines of darker color, increasing in number upward and finally 

 uniting in a network of orange-red bands an inch or more in 

 width enmeshing polygons and irregular figures of original 

 color one to five inches in diameter ; while still nearer the 

 surface the bands widen, the lighter colored polygons disap- 

 pear, and a nearly uniform orange- red hue supervenes. Yet 

 some of the lines of darker color persist as narrow bands of 

 brown, perhaps marking jointage planes ; and on closely ap- 

 proaching the surface these are frequently found to become 

 partially indurated, so as to form a network of embossed 

 chocolate-brown lines, enmeshing orange-red polygons. About 

 the points of union of the embossed brown bands the segrega- 

 tion of ferruginous matter and the cementation are most 

 decided ; and quite near to the surface the nuclei thus formed 

 may be found to graduate into irregular ferruginous nodules, 

 diminishing in size and increasing in hardness until they pass 

 gradually into the state exhibited by the surface-found concre- 

 tions. So the mottling, the darkening of hue, the general 

 ferrugination, and the formation of nodules are simple results 

 of oxidation and hydration produced by weathering. 



In Mississippi the Appomattox is well displayed at .Nicholson, 

 near Pearl river, and only 20 miles from the Gulf ; and 10 



