FEATURES OF THE TUSCALOOSA FORMATION. 589 



thought them newer than the Eocene white orbitoidal liniestone.''"^ Hilgard f 

 embraced this group in liis Eutaw, and called attention to the difficulty of 

 distinguishing it from the Drift or Orange sand. 



It is more than probable that much of Tuomey's Drift and Hilgard's 

 Orange sand is properly referable to this formation. As a matter of fact, 

 the discrimination is made with extreme difficulty, since the manner of 

 deposition and the general character of the materials is quite similar, con- 

 sisting of beds of more or less micaceous cross-bedded sands, water- worn 

 pebbles of chert and hornstone, together with lenticular masses of clay of vari- 

 ous colors. Tuomey I has shown the tendericy of the post-Tertiary Drift to 

 appropriate materials from the rocks over which it passes. The same may 

 be asserted of this, the Cretaceous Drift, and to this cause may be attributed 

 the marked differences between the character of the deposits in eastern and 

 western Alabama, since the conditions of sedimentation appear to have been 

 the same. 



From the Mississippi border to the water-shed between the Cahaba and 

 Alabama rivers, Smith's description § of these measures holds good : 



"'The most conspicuous rocks are purple and mottled clays interstratified with white, 

 yellowish-white, pink and light purple micaceous sands, and near the base of the 

 formation dark gray, nearly black, thinly laminated clays, with sand partings." 



But on leaving the Carboniferous rocks and the highly colored Paleozoic 

 shales the lithological features of the formation become marked by the ab- 

 sence of beds of gray and purple clay, while the pebbles consist no longer of 

 oolitic and fossiliferous chert, but of milky quartz, gneiss and schistose rocks. 

 In lieu of the thousand feet of material estimated || as occurring on the Tus- 

 caloosa and Alabama rivers, something less than a hundred feet is found on 

 the Chattahoochee, as follows : 



Section of Tuscaloosa Group ; C hattahoochee River. 



Base of the Eutaw group. 



Feet. 

 1 — Strongly cross-bedded coarse sand and pebbles, with some few fragments of 



schist and just enough white clay to hold the mass together. The quartz 



pebbles are well water- worn, while the softer bits of schist are but slightly 



abraded. This stratum varies in color from white to lemon-yellow and in 



places green, while tiie upper part becomes mottled purple and yellow. 



This last phase is strongly developed at Thomas bluff, Georgia, due east of 



Fort Mitchell, Alabama 40 



*lst Bienn. Rep. on Geol. of Ala., 1850, p. 116. 



fRep. on Geol. and Agric. Mis«., pp. 1860, 105-107, 66-68. 



t2d Bienn. Rep. on Geol. of Ala., 1858, p. 145. 



gBull. 43, U. S. Geol. Survey, 1887, p. 95. 



II Ibid., plate XXI. 



