304 GEOLOGY. 



are not uncommon. Irregular stratification is the rule, but some 

 portions are not bedded or laminated. Among such parts arc singular 

 lenses of sand which suggesl an eolian origin. While assortment 

 generally prevails, it is very often irregular and imperfect. A singular 

 pebble-earth that finds its analogue in subaerial and flood-plain deposits 

 is common, but, so far as we know, has no representative in marine 

 and lacustrine deposits. 



Color. — The coloration of the formation is significant, ranging 

 from brick-red through various pinks, purples, oranges, and yellows to 

 white. The color is more irregular than the composition, bands, 

 blotches, and mottlings diversifying the structural units. Where an 

 ancient, if not the original, surface of the Lafayette is preserved by 

 an overlying deposit, such as the loess, there is often a highly colored, 

 sub-surface zone, analogous to the sub-surface coloration of the later 

 deposits which cover it. This coloration is partly inherent in the 

 material, but more largely the result of a thin coating of red ferric 

 oxide enveloping the grains. Its significance is thought to lie in its 

 suggestion of the climatic conditions which accompanied or followed 

 the deposition of the formation, conditions under which the de posi- 

 tional action of sub-surface waters was greater than their leaching 

 effects. Such conditions are assignable to effective dry seasons. 



Partial removal of the formation. — Something has already been 

 said with reference to the general distribution of the Lafayette for- 

 mation, but it is not to be understood that it occurs everywhere within 

 the area specified. As a result of stream erosion the formation is 

 discontinuous. Over considerable areas, it caps divides, but is absent 

 from the valleys between them. In many places its remnants are 

 best preserved where the substratum is resistant rock, and less preva- 

 lent where the substratum is rock which is easily eroded. 1 



In Mississippi 2 and Alabama 3 a considerable belt underlain by 

 the Selma (Rotten) limestone is essentially free from the formation; 

 so also is the belt underlain by the Jackson or White limestone, and 

 the belt underlain by parts of the Lower Eocene 4 (Black Bluff, or 



1 Smith, Geology of Alabama, 1894. 

 2 Hilgard, Agr. and Geol. of Miss., 1860, p. 5. 



3 Smith, Geol. Surv of Ala., 1894, p. 68. 



4 McGee also points out the absence or meagerness of the formation over cal- 

 careous sub-terranes,12th Ann. Rept. IT. S. Geol. Surv. 



