660 LTE JOURNALVORNGLOLOGN, 
The gravel of Adams county is 175 to 200 miles north of the 
northernmost point where the high-level gravel has any consid- 
erable areal development. Within this distance, however, gravel 
is known at many points. At all these points its constitution, its 
physical condition, and its geological and topographical relations 
are such as to leave little room to doubt that the existing beds are 
to be correlated with each other, and that they are the erosion 
remnants of a once continuous formation, which extended over 
southern Illinois, reaching at least as far north as Adams county. 
The study of the high-level gravels of adjacent states had at 
that time (1891) left no room to doubt their correlation with the 
similar formations of Illinois. It is confidently believed that the 
gravels on the crest of Crowley’s ridge in Arkansas, and its con- 
tinuation northward into Missouri, are parts of the same forma- 
tion which once covered the southern portion of Illinois, and 
considerable parts of Kentucky and Tennessee. To the south, 
this formation probably extended to the gulf. Its extreme east- 
ward and westward borders, as originally developed, have not been 
determined, but in both directions the extension was great. In 
Indiana it is known to have reached as far east as Perry” county. 
The possibility should be recognized that these high-level gravels 
may not all belong to one formation, although the remnants thus 
far referred to in Indiana, Illinois, Missouri and Arkansas are so 
similar in constitution and in all their relationships as to raise a 
presumption in favor of this view. 
At the time of the reading of the paper cited above, the 
gravel had not been found at any place north of Adams county, 
Illinois. In spite of this fact, it was believed that the formation 
once extended further north since its materials, so it was 
thought, were to be recognized as minor constituents of the 
glacial drift at various points as far north as Rock Island county. 
If this identification be correct, it means that at the time of the 
deposition of the drift in Rock Island county, remnants of this 
preglacial gravel formation were still in existence as far north 
as that point. The localities in this county where material 
* Bull. Geol. Soc., Vol. III., 1892, p. 186. 
