~506 GEOLOGY OF OHIO. 
In view of the strikingly distinct character of these kames, I think we 
must conclude that they are comparative.y modern, and that they do not, 
as stated by Dr. Newberry, hold a definite place in the sequence of Drift 
phenomena. 
In accounting for them, two causes seem to be equally conspicuous, 
viz., currents of water and melting icebergs; and I do not know that 
they can better he described than in the words of the author quoted . 
above. “It seems,” he says, “that in the period of greatest submergence 
the larger part of the summit of the watershed was under water, and 
was swept by breakers and shore-waves, by which some of the beds of 
sand and gravel were formed, which are described under the head of 
kames; and I have supposed that a considerable portion of the materials 
composing these kames or eskers was derived from icebergs stranding on 
the shoals which now form the crest of the divide.” At this time suffi- 
cient depth of water existed in the passes of the watershed to float ice- 
bergs of considerable size. These, as they stranded along the slopes of 
the divide, or melted in their slow progress southward, discharged their 
immense cargoes of mud and gravel. When the water level had been 
somewhat depressed by the slow elevation of the continent, these gaps 
became, as I have supposed, waste-weirs, through which powerful streams 
of water continued to flow for a long time. These, constituting) the 
eddies, currents, etc., and the streams from the melting icebergs, have 
completed the sorting and shaping of he layers. 
Bowlders.—Nearly related to the ka: es in point of time and origin are _ 
the vast quantities of bowlders scatt.:red broadcast over the surface of 
the county. These are not to be confounded with the true glacial bowl- 
ders, which lie more or less deeply imbedded in the Drift, but are super- ° 
imposed, and owe their origin to floating ice.. Of the striated or glacial 
bowlders there appears to be two distinct epochs or systems in the Drift 
of Darke county, the first being marked by small (rarely ever large), 
dark-blue bowlders, finely striated and lying very deep, or upon the 
rocky floor of the Drift, the second lying in the yellow and bluish hard- 
pans and gravel to within five or eight feet of the surface, and embraced, 
probably, above a depth of twenty-five feet, containing the ordinary 
Drift rocks, with many coarsely-scratched limestones. The more mass- 
ive Drift bowlders belong to an entirely different class—that is, as to 
origin. Lithologically, however, they do not vary perceptibly from the 
latter of the true glacial rocks above mentioned, being chiefly green- 
stone, syenite, quartzite, diorites, dolomites, and other metamorphic 
rocks. They rarely if ever show glacial markings. [First we notice 
