CENOZOIC TIME — QUATERNARY, 967 



monodon, S. Mrsutum, Treodopsis appressa (Wetherby). The species are all of kinds now 

 living in the vicinity of the several localities. 



The shells of the lovpa lake are much below the natural size of the species, showing 

 the depauperating effect of the cold water (McGee) ; but in Kentucky those obtained near 

 the Mississippi are larger than those a few miles to the eastward (Loughridge) . 



3. Epoch of the Final Retreat. 



At the commencement of the Final Retreat, as shown by the position of 

 moraine B, ice still covered all New England, all New York, and very 

 nearly all that part of Pennsylvania that was covered at the time of maxi- 

 mum ice. But in Illinois and farther west to Dakota, the First Retreat had 

 left bare a broad belt, which extended northwestward into British America 

 west of Manitoba. 



In the Final Retreat the Mississippi valley was still, compared with the 

 east, the region of most rapid melting, and for the same reason as before — 

 the warmer and drier climate. The series of loop-shaped moraines in Illi- 

 nois and Wisconsin, and that in Iowa and Minnesota, mark the succession. of 

 halts and recessions in the course of the retreat northward from the moraine 

 line B. 



The Illinois series, as described by Chamberlin and Leverett, covers 

 much of Illinois and passes thence into Wisconsin ; and the Iowa-Minnesota 

 series, as mapped by Upham, extends first northward and then over Minne- 

 sota northeastward, for more than 400 miles. In addition, the retreat was 

 going on from the moraine line B in Assiniboia, north of Montana, laying 

 bare much of Manitoba. 



In the Illinois series of moraines, there is near Madison the noted Kettle 

 moraine (KK on the map), more than 200 miles from the line B, or that 

 of the Shelbyville moraine. But in Indiana the distance of retreat between 

 the moraine line B and the line K, or that of the Kettle moraine, narrows 

 rapidly ; and in Ohio it is very small, the first moraine north of the moraine 

 B being regarded by Chamberlin and Leverett as probably the moraine K. 

 Farther east, moraine K extends along with moraine B into western New 

 York. It has been supposed by Chamberlin to pass probably south of 

 Cayuga and the other Finger Lakes, In view of the nearness to the line B 

 in Ohio, it may be questioned whether it does not take the same oblique 

 course with it through Pennsylvania and become there indistinguishable 

 from it ; and the same also farther eastward across New Jersey and south 

 of New England. If this is the right view, New England held to its ice 

 during all the retreat in Illinois of 200 miles, precipitation to the eastward 

 adding about as much ice as was lost by the melting. 



Subsequently the final retreat involved the Eastern States as well as the 

 Mississippi valley, and moraines over New England and New York mark 

 its progress. One, as described by R. S. Tarr, crosses Massachusetts west of 

 the Connecticut, passing south of Turner's Falls, Orange, Royalston, Win- 

 chendon, and terminates in the Cape Ann moraine described by Shaler" 



