HURON COUNTY. 291 



comminuted debris has been intimately mixed with that of the granite 

 of the north, and of all the intervening rocks, and the whole spread out 

 over the surface of the county. As the waters which covered the surface 

 at the close of the glacial epoch receded, each of the terraces described 

 above was formed, and each for a long period constituted a shore swamp, 

 in which the decomposing vegetable material accumulated to form a soil 

 of unsurpassed and permanent fertility. 



The materials composing the upper terraces were long subjected to the 

 action of shore waves, and in places the surface is occupied by sand dunes 

 and assorted gravel. The lower terrace is a broad prairie, with s-^ampy 

 muck soil. When the country was first settled, some of this was not 

 suflBciently reclaimed from the water to support forest trees, but the 

 greater part of it is now remarkably fertile farming land, especially 

 adapted to the cultivation of corn. In a few places the prairie soil rests 

 upon the bed-rock, but generally upon a heavy deposit of boulder clay, 

 containing the ordinary granitic and metamorphic boulders, and also a 

 great profusion of fragments of limestone ; and wherever gravels are found 

 a large percentage of the pebbles is derived from the limestone. Indeed, 

 the Drift deposits here all contain an unusual abundance of the debris of 

 the limestones. In the bed of Huron River are many large boulders of the 

 Corniferous limestone. In the sand hills the cavities left by decaying 

 roots are often filled with calcareous tufa, and crumbled and broken layers 

 of the Berea grit in the quarries are frequently cemented into a coarse 

 breccia by the percolation of lime water from above. Also the beds of 

 water-worn pebbles are here and there cemented into a conglomerate by 

 the same cause. To these facts, together with the abundance of humus 

 from the old swamps which once covered the surface, we must attribute 

 the remarkable fertility of a large part of the county. 



The general elevation of the level prairie land in Lyme township is 

 one hundred and twenty-five feet above the lake. Here is a succession of 

 remarkable sand dunes which rise to the height of thirty feet. The sand 

 composing them is fine, shows^irregular, waved lines of stratification, and 

 rests upon peat. These sand hills were formed, as was much of the main 

 sand ridge of the county, by wind and wave action along the lake shore, 

 and on the margin of a shore swamp caused by this barrier, in which 

 vegetable debris accumulated for a long time. The swamp soil in many 

 places contains abundant remains of corniferous trees, and extends under 

 the dunes and the sand ridge, because the sand was drifted back from the 

 beach over it. The north and south bases of the ridge and sand hills 

 have the same elevation above the lake. The north side of the ridge 

 exhibits the irregular, winding outline of k lake beach, while on the 



