POSTGLACIAL BIOTA OF THE GREAT LAKES REGION 139 



Lampsilis luteola Goniobasis livescens 



Sphaerium striatinum Gatba elodes 



5. Deposits of Uticertain Age 



There are a multitude of lakes in Michigan which contain ancient marl beds 

 referable to some one of the lake stages. As these deposits cannot be correlated 

 with any of the known beaches it is impossible to refer them definitely to any 

 period of the lake history. They are probably to be classed as of Nipissing 

 age, tho some may be as old as Algonquin time, or even older. Nearly all of 

 the shell-bearing strata are covered with peat deposits of greater or less thick- 

 ness, showing that there has been a shallowing of the water since the formation 

 of the lakes. 



Russell and Leverett 60 describe a marl deposit beneath 5 feet of peat, in 

 swamp} 7 territory three miles south of Ann Arbor, containing mollusks, as 

 well as a skull of Castor oides. The species of mollusks are indicated below: 



Valvata sincera Carychium exiguum 



" tricarinata Succinea avara 

 " tricarinata confusa " retusa 



Physa a-ncillaria Strobilops affinis 



" Integra Polygyra monodon 



" gyrina hildrethiana Helicodiscus parallelus 



" elliptica Pyramidida cronkhitei anlkonyi 



Planorbis campanulalus Zonitoides arborea 

 " hirsutus " minuscula 



" exacuous Eiiconulus fidvus 

 " parous " cher sinus polygyratus 



Galba obrussa decampi Vitrea hammonis 



The absence of pelecypods and the presence of so many land mollusks 

 (nearly 50 per cent) is noteworthy. The deposit was either formed in shallow 

 water or near the shore. It is extremely difficult to correlate the age of these 

 deposits with that of any of the lake stages. The swamp is from 820 to 826 

 feet above the sea, which is several feet above the highest beaches of the ancient 

 lakes. The life may have been contemporaneous with Lake Warren, possibly 

 correlative in time with the formation of the Forest beach. 



The presence of extinct mammals in the same deposits is evidence of their 

 comparative antiquity. Bones of the mastodon as well as of Castor oides have 

 been obtained and are preserved in the museum of the University of Michigan. 

 Several molar teeth of Castor oides were also found between the Ann Arbor Rail- 

 road and Packard Street, in meadow land. This same swamp (but in later 

 deposits) has yielded the bones of the elk, deer, and other vertebrates, and we 

 may well conceive that in former times these and other animals frequented 

 this region and became mired in the swampy portions of the lake. 



80 Ann Arbor Folio, p. 9. 



