14 Frank Carney 



tremely stony till (figs, i, 2, and 6^"). I have nowhere noted a 

 gradual blending from one color to the other, nor streaks of the 

 yellow penetrating the bluish, as has been described in the Central 

 West.^^ It is very likely that upon sufficient exposure to weathering 

 agents the blue till would become lighter in color ; but because of its 

 indurated condition it weathers less rapidly than does the superficial 

 Wisconsin drift. 



2. An ice-cap passing over glacial sediments, particularly till, 

 develops in its joints and faults (figs. 2-4) either because the till 

 on account of inconsistency in structure yields differentially to the 

 weight, or because differential strains are induced by topography ; 

 these fracture lines are approximately vertical (figs. 5, 6). I have 

 observed this jointed condition of till in central and northern Ohio, 

 and in New York along creeks tributary to the outlet of Keuka 

 Lake.^-* 



3. The altered drift described in this paper contains abundant 

 carbonates, probably deposited from circulating ground water, 

 whereas carbonates are either absent or less conspicuous in the 

 superjacent drift of later origin. This difference between the two 

 drifts is apparent even when tests are made near their contact; the 

 observation holds for exposures studied in all the areas under con- 

 sideration. 



4. The color in the case of the drift above described, its 

 indurated condition, and the jointing appear to be associated with 

 the change or metamorphism which develops tillite from glacial 

 drift. 



5. I believe that so far as the regions considered in this paper 

 are concerned two Pleistocene epochs are indicated by. a contact of 

 the bluish and yellowish till. 



12 Cf. Journal of Geology, vol. XV (1907), pp. 575, 577, for other pictures illustrating 

 the same variation in texture. 



13 F. Leverett, Monograph XLI. U. S. Geolog. Surv. (1902), p. 272. Ibid., Monografh 

 XXXVIII, U. S. Geolog. Surv. (1899), p. 28. W. H. Norton, Iowa Geological Survey, 

 vol. IX (1898), pp. 480-82. 



li Journal of Geology, vol. XV (1907), pp. 583, 584. 



