CHAPTER II. 



GEOLOGICAL STRUCTURE OF THE LOWER PENINSULA. 



{Surface Material?) 



The entire surface of the peninsula is covered by heavy drift 

 deposits, with the exception of a few limited localities, in which the 

 drift, subsequent to its deposit, has been washed off by floods, or 

 by rivers carving their courses deep enough to touch the rock beds 

 of older formations. These drift masses are nearly the same in 

 character as those described from the Upper Peninsula in the first 

 volume of the geological reports. The material has been changed 

 somewhat by an admixture of rock debris from the formations en- 

 countered by the moving glaciers in their southward course. The 

 glacier drift spread itself in a compact body over the entire surface 

 of the Lower Peninsula, in evidence of which fact the rock beds, 

 wherever they are found denuded, and the nature of the rock has 

 been capable of preserving the marks, bear the traces of its motion 

 on their scratched surface. Not all the drift material found on the 

 lower peninsula has been transported there by glaciers ; a large pro- 

 portion of it must have been carried southward by water, partly in 

 suspension, as mud and sand, partly frozen into floating ice, as the 

 coarser material, the gravel and boulders. 



The glaciers deposited moraines, heaps of rubbish composed of 

 all kinds of rock debris in every degree of comminution from the 

 large boulder down to the impalpably fine clay. Much of the drift 

 is not found in this orderless form of moraines, but is disposed in 

 well-stratified layers, assorted according to the weight of its parti- 

 cles by water-currents. It is suggested that floods, acting subse- 

 quently on the masses of the moraines, sifted and washed the light- 

 er transportable particles out of them, to deposit them elsewhere 

 as layers of clay, sand, or gravel, but this can not explain all the 

 phenomena we observe In the arrangement of the drift material. 

 We find large boulders, some of them many tons in weight, in 



