294 E. A. Smith — Post-Eocene Formations of Alabama. 



ings favor the other. On any theory yet offered, there are 

 many phenomena difficult of explanation. 



That the Lafayette-coated surfaces have suffered a great 

 amount of denudation is everywhere plainly to be seen, and 

 that the amount of this denudation increases with distance 

 from the sea may, I think, also be shown. This would lead 

 us to conclude that the deposition of the Lafayette extended 

 over a long period of time, and that the landward margins of 

 the area covered by it were being denuded while accumulation 

 was still going on further to seaward. Thus, we find upon 

 some of the hills of the Coal Measures in Alabama (Walker 

 County) a good many miles northward from the main mass of 

 the pebbles, etc., covering the junction of the Paleozoic and 

 Cretaceous formations, occasional small remnants of the Lafay- 

 ette in the form of thin beds of pebbles and sands, capping 

 some of the highest summits, while all trace of this formation 

 has disappeared from the adjacent valleys. Over the Cretace- 

 ous terranes there are many spots entirely bare of Lafayette, 

 and the same is true of some of the lower members of the 

 Eocene, but over the newer Eocene and the whole Miocene 

 area the covering of Lafayette seems to be not only continuous, 

 but also of greater thickness than over the older formations. 

 Where it comes down within a mile or two of the coast, as in 

 the divides of Mobile and Baldwin Counties, the thickness can- 

 not be less than 100 feet and. it may be more. Over the entire 

 coastal plain the thickness cannot average more than 25 feet, if 

 so much. 



Concerning the age of the formation, we know certainly 

 that it lies between the upper Miocene and those beds of 

 undoubted Pleistocene age which we have described under the 

 name of Second Terraces. If the phenomena of glaciation be 

 taken as the criterion of the Pleistocene, then the Lafayette 

 would have to be classed as Pre-Pleistocene, since yellow gravel 

 beds, presumably of this age, have been traced up to and 

 underneath the oldest of the Glacial deposits, and as yet the 

 existence of materials of Glacial origin among the Lafayette 

 beds seems not to be proven beyond question. 



And further, the general appearance of the formation and 

 the demonstrably great amount of erosion which it had suf- 

 fered before the deposition of the undoubted Pleistocene beds, 

 would lead us to conclude that a long period of time and im- 

 portant physical changes 02curred between the accumulation of 

 the Lafayette and of the Pleistocene deposits. On the other 

 hand, the phenomena of the distribution of the Lafayette beds 

 and their manner of accumulation, so utterly unlike those of 

 any of the earlier Tertiary formations of the Gulf coast, make 

 it difficult to fit the Layfayette into the Tertiary. 



