506 GEOLOGY OF OHIO. 



In view of the strikingly distinct character of these kames, I think we 

 must conclude that they are comparatively 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 

 thej"^ can better be 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 conpiderable 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 plow 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 kar es in point of time and origin are 

 the vast quantities of bowlders scattered broadcast over the suiface 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 flnalivg 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 ijnng 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 



