486 FRANK CARNEY 
where it forms a riffle. These localities are just within the margin of 
the Wisconsin drift, where the ice was attenuated as well as short- 
lived. It is certain that in these two cases time has been the important 
factor in the alteration; no great mass of ice ever stood here for even 
a short period. If this hard bluish till was deposited by Wisconsin 
ice, its color is genetic; but on this hypothesis it is difficult to under- 
stand why the superjacent drift is yellowish, and the line of division 
is so sharp. 
But there can be no question that the old valley of Rocky River, 
west of Cleveland, was buried by a pre-Wisconsin ice-invasion, pre- 
sumably the Illinoian. The bluish till in this buried stream-course 
is apparently identical with the dense drift referred to in central Ohio 
and New York. 
These facts suggest the following conclusions: 
t. Glacial deposits, regardless of their constituents, when buried 
for a long time appear to become compact, and bluish in color. This 
assumption does not disregard the possibility that some deposits 
have always been bluish. The dozens of exposures studied in both 
states show a great variety of rock-constituents, as well as wide varia- 
tion in the general texture of the drift; this color is constantly noted 
in drift ranging from fine silt to an extremely stony till (Figs. 1, 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 it joints and faults (Figs. 2-4) either because the till on 
account of inconstancy 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 
« Cf. Journal of Geology, Vol. XV (1907), pp. 575, 577, for other pictures illustrat- 
ing the same variation in texture. 
2 F. Leverett, Monograph XLI, U. S. Geolog. Surv. (1902), p. 272. Ibid., 
Monograph XXXVIII, U. S. Geolog. Surv. (1899), p. 28. W. H. Norton, Jowa 
Geological Survey, Vol. 1X (1898), pp. 480-82. 
