GEOLOGICAL CHANGES IN MICHIGAN. 829 



the mimic tracks made by light objects that are moved along by the 

 wind, such a scene is in itself a study for a naturalist. 



In some places, Lake Michigan is year by year building out the 

 land with fresh deposits of sand, but oftener it is cutting it away with 

 every storm. A reach of coast, extending perhaps a mile and a half 

 southward from the foot of White Lake, is particularly interesting to 

 one who wishes to study the structure of the country. Here, of late 

 years, the lake has been eating away the land. The bluff facing the 

 water is from fifty to one hundred and fifty feet high ; sometimes its 

 face is covered from top to bottom with earth that has slid down so as 

 to conceal its structure, at other times this is all swept away and the 

 strata are revealed. At such times an old surface-line of vegetable 

 mold may be seen through the entire extent of the section at a height 

 of from ten to twenty feet above the lake. Above this line all is sand, 

 below it all is a heavy solid earth, of which clay forms the principal 

 part. In the depressions of this line, where channels of drainage in 

 this ancient line of surface may be supposed to be cut across, springs 

 flow out. In one such depression there is a bed of peat, marking the site 

 of an ancient swamp, and near each edge of this bed it is full of timber 

 that has fallen into it when a swamp and there been preserved. Some 

 of this wood seems to be but little changed, while other pieces have 

 almost the color and texture of charcoal. Here we have found elm, 

 oak, and black-ash, the species of which might be recognized as easily 

 as if just from the forest. Some branches had been charred by fire, 

 and altogether the deposit is exactly what we might expect to find in 

 the edge of a Michigan swamp of the present day, with the difference 

 that this has been compacted and hardened by time and pressure and 

 drainage. The clay soil in which this old swamp was situated seems 

 to underlie the sand everywhere in this region at varying depths, but 

 on excavating to it we do not everywhere find the vegetable mold 

 that here marks its surface. From these facts the conviction has grown 

 that here in Western Michigan the condition of things has varied some- 

 what like this : First succeeding the introduction of the present order 

 of things at the close of the last Glacial epoch, the entire country was 

 at an elevation above Lake Michigan much greater than at present, 

 great enough to drain the bottoms of all these river-lakes which, it 

 should be noticed, are deepest near the great lake, and generally termi- 

 nate in a swamp at their head, and each of which is elongated in the 

 same general direction as the valley the foot of which it occupies. 

 This condition of things lasted until the configuration of the land had 

 become substantially what it is at present ; then a subsidence took 

 place, until all the lower levels of the country were beneath the waters 

 of Lake Michigan. Again the country began to rise, and as the sub- 

 merged lands were lifted above the water they were covered with 

 sand, exactly as the lake now deposits sand on a retreating coast. 

 When this uplifting reached such a degree that the action of the 



