THE GEOLOGICAL SECTION OF MICHIGAN 429 



leveled off, and even the harder felsites and granites did not rise 

 more than four or five hundred feet above the general level. As 

 we find fragments of Upper Cretaceous not far^^pff in Minnesota 

 on the Mesabi Range we are inclined to put the culmination of this 

 period of leveling at that time.^ 



On the other hand, deeply incised valleys and caves in limestones 

 suggest a period of high level in the Tertiary between that time and 

 the ice age. Some time someone may find in the prosecution of the 

 limestone quarrying, around Fiborn or Alpena or Monroe in the 

 caves upon which one comes, vestiges of Tertiary cave life. I do 

 not know of any yet. 



PLEISTOCENE AND RECENT DEPOSITS. I,IIO-0 FEET 



Michigan is so near the center of the latest glaciation and that was 

 geologically so recent, the effects of ice blocking the St. Lawrence 

 valley having lingered so far as one can judge until within a few 

 thousand years, that it does not seem sensible to divide the Glacial 

 and Pleistocene from the present. Mammoth and ^mastodon bones 

 are found within a few inches of the surface and where forest clad, 

 the topographic forms left by the ice are almost as sharp as when left, 

 with much less alteration than 50 years of farming make. However, 

 beds of peat 30 or 40 feet thick, of boglime, lacustrine, and alluvial 

 clays 14 feet thick and perhaps more have accumulated and forma- 

 tions like the delta of the St. Clair flats, Tawas Point. So far as we 

 can estimate none of these post- Glacial deposits need have taken over 

 10,000 years. 



The greatest thickness of the Glacial-Pleistocene deposits we may 

 estimate to be 1,110 feet near the north line of Osceola County, 

 southeast of Cadillac. But the greatest thickness actually measured 

 is in the deep wells near by on the Lake Michigan shore at Manistee 

 and Ludington, where the rock surface is below sea-level, but they 

 can hardly be separated systematically in a geological column. 

 Both in the character of the pebbles, however, and in other ways, 

 a transportation from the northwest as well as the northeast is plainly 

 indicated, and at least one period between the two during which red 

 lake clays were in some places laid down.^ 



1 Schuchert, Pis. 94-95. 



2 Report for 1906, Russell on "Surface Geology," 43, 73; Rominger, I, Part III, 17. 



