CENOZOIC TIME — QUATERNARY. 965 



Mississippi on either side, of tlie Tombigbee and Tennessee, as well as of 

 the Sabine, there is a steady increase of gravel. It occasionally contains, 

 even in Mississippi, stones of 10 to 100 pounds in weight, and rarely 150 

 pounds. There are also some local clayey beds. The stones show that the 

 material came from the northward ; many have in them Paleozoic fossils. 

 The beds are irregularly stratified, sometimes structureless for 20 feet of 

 thickness, but have generally the Jtow-and-plunge structure, illustrated in 

 Fig. 63, page 93. The facts prove, as Hilgard states, that there was a vast 

 and violent flow of waters down the broad Mississippi valley, bearing an 

 immense amount of sand and coarser detritus, and also some floating ice 

 for the transportation of the larger stones. Hilgard therefore concluded 

 that it must have been made during the melting of the ice, while the conti- 

 nent had still the elevation characterizing the Glacial period. These condi- 

 tions are those of the First Ketreat. 



There were cotemporaneous depositions from streams descending the 

 Atlantic and southern slopes of the then snow-clad Appalachians ; and large 

 areas of the Lafayette formation in these regions and elsewhere have been 

 defined and mapped by McGee. 



The "Orauge sand " is often 40' to 100' thick, and in some places over 200' according 

 to Hilgard, and toward the Gulf it has still greater thickness. In an Artesian well, near 

 the Calcasieu River, 200 miles west of New Orleans, beds referred to the Lafayette are 450' 

 thick, beneath 160' of clay of the Port Hudson group; and at New Orleans 760'. This 

 thickness along the Gulf is supposed to be evidence of a gradual subsidence of its bor- 

 der to the great depth stated, as deposition went forward. 



The actual limit of the formation is in doubt because it contains no fossils, and the 

 criterion usually appealed to in its correlation, — kinds and color of gravels, — is admitted 

 to have, whatever the rock series, almost no value. In Texas, some beds referred to the 

 Lafayette were found by G. D. Harris to contain Tertiary fossils. 



In his early account of the formation, Hilgard stated, on the authority of Tuomey and 

 LeConte, that the formation passed from Alabama eastward, around the higher Appa- 

 lachian highlands into the Carolinas, and thence north to Virginia and Maryland. McGee 

 described, in 1888, similar beds of orange-colored sands and clays along the Appomattox 

 River and other points in Virginia, and also others, in North Carolina and beyond, to which 

 he gave the name of the Appomattox formation, and he has since studied the beds in the 

 Mississippi valley. He argues that part of the borders of the Atlantic and Mexican 

 Gulf were 200' to 800' below their present level at the time, making the beds in part 

 marine. No marine fossils or other marine relics have been described in evidence of the 

 submergence. Moreover the formation is made preglacial by McGee, and others. 



The term Lafayette was substituted in 1892, by agreement, for the older names of 

 Orange sand and Appomattox. 



Mr. Hilgard's last paper on the subject is in the A^n. Jour. Sc, xliii., 1892; and 

 Mr. McGee's first on the Appomattox in Am. Jour. Sc, xxxv., 1888, and his last on the 

 Lafayette formation in vol. xii., Bep. U. S. Geol. Surv., 1892. 



3. River channels filled by the drift. — The discharge of drift from the 

 melting glacier sometimes filled up and blocked river channels at places, 

 and compelled the river to make a new cut. 



The Ohio River, according to Newberry, formerly had a more southern 



