390 K W. Hilgard — Age and Origin 



" Orange Sand," that the latter lias been deposited on a deeply 

 denuded surface. The latter fact is also shown in numerous 

 profiles, and is the rule in the interior uplands ; while near the 

 larger river troughs, and notably in a north-and-south direction, 

 the unconformity is less conspicuous and the lower limit of the 

 formation is less uneven. In the southern portions of Missis- 

 sippi and Louisiana, the rolling plateaus that bear the great 

 long-leaf pine forest, are underlaid by the formation some- 

 . times to the depth of over 200 feet. It reaches the Gulf shore 

 at only a few points ; in Mississippi near Shieldsboro', where 

 prominent ridges abut on the coast plain on Pearl river about 

 20 miles above its mouth. In Louisiana the shore is reached 

 at the Island of Petite Anse, where it immediately overlies the 

 (doubtless Cretaceous) rock-salt deposit. Within the last few 

 years it has been proved to reach the shore of Mobile Bay, by 

 Lawrence Johnson. 



The material of the formation, away from large channels 

 and from contact with underlying beds, is predominantly a 

 ferruginous (sometimes more or less clayey), hence usually 

 orange or rust-colored, but sometimes purplish, white or varie- 

 gated sand, consisting almost entirely of quartz grains much 

 rounded and smoothly polished, and very commonly incrusted 

 with the rusty pigment. This external character of the sand 

 is popularly so well understood that building contracts ex- 

 pressly provide for " river or creek " sand, prohibiting the use 

 •of that formed of the smooth, round grains for mortar. Near 

 the surface of the formation this sand is commonly more or 

 less commingled with the surface loam or its washings ; while 

 where it overlies clayey formations of whatever age, it is com- 

 monly more or less commingled with similar clays (more or 

 less altered), whether by inter-bedding, intermixture, or very 

 commonly by the inclusion of rounded clay fragments, ranging 

 in size from mere grains to bowlders of a foot or more diameter. 

 Where in contact with sandy formations, the lower portions of 

 tbe "Orange Sand" (identified as such by the peculiar bed- 

 ding, and unconformity with the underlying older beds), com- 

 monly consists of the materials of such beds, re stratified in the 

 manner of the later formation. 



Near the great river channels, notably that of the Mississippi 

 on either side, on the Tombigbee and Tennessee, as well as on 

 the Sabine, there is a steady increase of gravel ; shown con- 

 spicuously on the landward margin of the Loess belt of the 

 Mississippi, as well as, at numerous points, close to the river 

 itself ; and (near the line between the states of Mississippi and 

 Louisiana) eastward to Pearl river and Lake Pontchartrain. 

 Conspicuous gravel deposits lie along the lower course of the 

 Tennessee river, in Mississippi and Tennessee. 



