THE OSAR GRAVELS OF THE COAST OF MAINE. ^ 



In the interior of Maine we find the long osars interrupted 

 near the tops of transverse hills crossed by the glacial rivers, 

 and still more interrupted on steep southern slopes. In such 

 situations it is evident that the velocities of the osar rivers would 

 be greater than the average, with the result that the rivers swept 

 their channels clear of sediments. The conditions were those of 

 transportation by the glacial rivers rather than deposition. 



If we follow the osars southward toward the ocean we find at 

 about the average distance of thirty miles from the shore that 

 the osars begin to be interrupted in a different manner from that 

 in the interior. Gaps begin to appear in the ridges in level ground 

 where the land slopes could not cause an accelerated motion of 

 the glacial rivers. Indeed, the gravels more often appear on the 

 tops of low hills than in the lower grounds. Going southward 

 the sizes of the ridges become on the average smaller, their mate- 

 rials rather coarser, the intervals longer, and finally near the north- 

 ern ends of the bays or fjords of the coast they disappear. If 

 they continue farther southward or into the sea, it is in masses 

 that are so small as to be covered out of sight by the marine 

 beds. The coastal towns are usually covered by clays, and road 

 gravel is often in great demand. The vigilance of town ofificers 

 has often detected beneath the marine clays small mounds of 

 gravel that form the southern ends of gravel systems. To the 

 south we reach a region where no gravels have been found. 

 When we find an osar system graduating into mounds so small 

 that not even the selectmen of a Maine town can find water- 

 washed road gravel, we may be sure that our osar has come 

 practically to an end. I have examined the charts of the Coast 



I Condensation of chapters of a report on the Glacial Gravels of Maine, written for 

 the U. S. Geological Survey. 



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