THE PLIOCENE PERIOD. 301 



The similarity of these gravels to the Lafayette farther south sug- 

 gests their correlation with that formation. Perhaps a better view 

 is that they are the older part of the complex series of river deposits, 

 shifted repeatedly to lower levels, and nearer the sea, until the main 

 part of the series is now near the coast, while only meager remnants 

 remain in the sites of original deposition. The farther these remnants 

 are from the low coast -plain the smaller they are and the greater their 

 altitude, and if the above interpretation be correct, the greater their 

 age. In other words, the remnants become larger, lie at lower levels, 

 and are presumably younger, to the southward, where they seem to 

 grade down to the more continuous Lafayette formation soon to be 

 described. 



The patches of gravel here referred to are found in Minnesota, 1 

 Wisconsin, 2 Iowa, Illinois, 3 Arkansas, 4 Indiana, 3 Kentucky, and Ten- 

 nessee. The leading topographic features of the Mississippi basin 

 have been developed since the deposition of these gravels, for their 

 northern remnants are on the crests of the highest lands within the 

 areas where they occur. 



Reference was made to the phase of deposition here set forth in 

 connection with the Potomac series (p. 112), and the phenomena 

 seem to have been repeated in the same region, in much the same 

 way, in the Pliocene, giving rise to the Lafayette formation, known 

 earlier in the Mississippi basin as the Orange sands. This formation 

 has been, and still is, the occasion of so much difference of opinion 

 that it merits special consideration. It should be said, in prudence 

 and fairness, that the interpretation here given it is not unchallenged, 

 and the alternative views will be indicated later. 



The Lafayette Formation. 5 



The Lafayette formation has an extensive distribution between the 

 Appalachians and the Atlantic, and in the Mississippi basin, and is repre- 



1 24th Ann. Rept. Minn. Geol. Surv., p. xxv. 



2 Jour, of Geol., Vol. Ill, p. 655. 



3 Bull. Geol. Soc. of Am., Vol. Ill, p. 183; see also references given in this paper. 



4 Geol. Surv. of Arkansas, Report on Crowley's Ridge, and also Am. Jour. Sci., 

 Vol. XLI, 1891, pp. 359-377, and Vol. XLII, p. 252. 



5 The fullest account of this formation as a whole is that of McGee in the Twelfth 

 Annual Report of the U. S. Geological Survey. Referenceo to other accounts of 

 the formation in special localities, often under other names, are as follows: Safford, 



