214 L. C.Johnson — Grand- Gulf Formation of Gulf States. 



Adjoining the Great River, the "Grand Gulf" formation 

 is covered first by the sands and gravels called by Dr. Hilgard 

 " the Orange Sand ;" and this is overlain by his " Port Hud- 

 son " and loess. At a dip, estimated as between twenty and 

 thirty feet to the mile, the average thickness must approxi- 

 mate two hundred feet. 



Though a geological examination of this obscure portion of 

 our Gulf terranes has only commenced, the relation of the 

 "Grand Gulf" to the underlying and overlying formations, 

 having within the last three or four years been called in ques- 

 tion, some recent observations on the line of the calcareous 

 Eocene outcroppings may be of general interest. 



As already intimated, there is no dispute as to later strata. 

 The so-called " Orange-Sand," at least to the west, covers the 

 " Grand Gulf " to unequal depths. Many sections in Clai- 

 borne, Jefferson and Adams Counties, Miss., on the smaller 

 tributaries of the Mississippi, exhibit the great gravel beds 

 assigned by Dr. Hilgard to his " Orange Sand," resting upon 

 it, as the loess there rests upon the gravel. Underlying it, we 

 are not so fortunate as to possess many satisfactory exposures. 

 The relations here were rather an inference on the part of Dr. 

 Hilgard, founded upon general principles, and not from 

 instances of actual visible contact. It has even been said that 

 no locality shows exactly the relative position of the two, so as 

 to prove conclusively Dr. Hilgard's hypothesis. Mr. Otto 

 Meyer thought he saw a contact of these in a cut of the Ticks- 

 burg and Meridian Railway, near Pelahatchie, Miss., and he 

 regarded it as proof of his hypothesis that the " Grand Gulf " 

 is the older, and that the superposition is the other way. 



Having traced the course of the Eocene rocks across several 

 counties of Mississippi, and seen the exposures on almost all of 

 these small rivers and railroad cuts, I have no doubt whatever 

 of the correctness of Dr. Hilgard's views. Had no locality of 

 actual contact been found, the evidence would still be satis- 

 factory, for in every instance in this State, and in Alabama, 

 and in Louisiana, where the stratification could be observed of 

 either of these formations, the dip has been found uniformly 

 southward. 



To set all questions aside, at least one point of actual 

 contact has been found. As a general rule, the streams of this 

 region run southward, and cut across the structure of the 

 formations, but they fail to make many bluffs, and these not at 

 points to expose the strata and their relative positions. On 

 Chickasawkay River, however, the bluffs, which extend in 

 almost unbroken series for more than twelve miles between 

 Shubuta and Winchester, display every layer from the former 

 in the middle of the Jackson formation to Brown's Bend in 



