314 . PLEISTOCENE OF INDIANA AND MICHIGAN. 



at several miles back under the ice, and where drumlin forming was going on this is likely to 

 have been a potent factor in determining texture and compactness of the material. 



BURIED LACUSTRINE (?) CLAYS OP GRAND TRAVERSE REGION. 



Distribution. — Beneath the latest till deposits of the eastern coast of Lake Michigan from 

 the vicinity of Frankfort northeastward nearly to the Straits of Mackinac there are frequent 

 exposures of a clay which is nearly free from pebbles and which appears to have been deposited 

 in water. In some of the exposures the clay is distinctly laminated and is evidently water 

 deposited. In other exposures it was difficult to discover bedding planes, yet the absence or 

 extreme scarcity of pebbly material renders the clay a doubtful glacial product. In a few places 

 there are sandy partings between the layers of clay, and in such places the deposition in water 

 is scarcely to be questioned. These clay deposits are present in the abrupt bluff-like borders 

 of some of the deep valleys or valley -like lowlands which traverse this region. These. lowlands 

 ordinarily contain a great depth of loose sand, and it is not known whether this sand is underlain 

 by the clay. 



The altitude which the clay reaches beneath the crests of the ridges is difficult to determine. 

 Exposures on the slopes of the ridges, by which it has chiefly been discovered, show it to be 

 present south of Central Lake and southeast of Pine Lake in the vicinity of Boyne Falls up to an 

 altitude about 300 feet above Lake Michigan, or 880 feet above sea level. West of Bellaire 

 and near the northern end of the peninsula hi eastern Emmet and western Cheboygan counties 

 it was noted about 850 feet above sea level. Between Torchlight Lake and Grand Traverse Bay 

 and on the peninsula between the arms of Grand Traverse Bay it is found up to a height of 800 

 feet or more. In the vicinity of Frankfort and northeastward past Crystal Lake and Platte 

 River the highest exposures are between 680 and 740 feet above tide. Several exposures were 

 noted in the vicinity of Benzonia. Exposures are good in Frankfort along the shore of Lake 

 Michigan and also in excavations near the courthouse. 



Structure and characteristics. — This laminated clay varies considerably in color In the 

 vicinity of Frankfort, north of Pine Lake and northeast of Little Traverse Bay, it is red or pink. 

 Along the east side of Grand Traverse Bay and near Central Lake on the west side of the west 

 arm of Intermediate Lake much of it is drab or blue. The pink color seems likely to be due 

 to the accession of ferruginous material from the formations in the northern peninsula, just as 

 in the overlying till. The drab or blue is the ordinary color presented by deposits that have 

 received no special contribution of red ferruginous material. 



This clay is generally very calcareous, whatever its color. Much of it shows calcareous 

 nodules and tubes on the face of the exposures. The deposit appears, therefore, to have received 

 such a fine flour as is produced by the grinding of limestone formations by an ice sheet. 



The thickness of the deposit differs widely, ranging from a few feet to 100 feet and pos- 

 sibly much more. The record of the boring at Elk Rapids suggests its presence to a great 

 depth below the level of Lake Michigan, and exposures a few miles northeast of that village 

 show its presence more than 200 feet above the lake. 



Origin. — Much uncertainty exists as to the origin of this clay. Its range in altitude and 

 its possible thickness are greater than seem easily attributable to ordinary lake action, and yet 

 such may be the method of its deposition. Possibly before the ice made its final recession from 

 this region the northern end of the southern peninsula of Michigan was low enough for the lake 

 waters to cover all the places in which the clay has been found, although some of these are 300 

 feet above present lake level and about 200 feet above neighboring portions of the Algonquin 

 beach, the beach of the first glacial lake that succeeded the final recession of the ice. Since 

 Algonquin time there has been an uplift of only about 100 feet in the region bordering Little 

 Traverse Bay, but there may have been a much greater pre-Algonquin uplift. The pre- Algonquin 

 uplift, as shown in the tilting of the Arkona, Whittlesey, and Warren beaches, seems sufficient to 

 support the view that if free from ice in Lake Arkona time the region in which these buried 

 silts are present would have been covered by lake waters to about the extent which these silt 

 deposits reach. 



