Summary. 
509 
lobe of the latest drift formation. This terminal moraine is 
clearly older than the Kettle moraine, being overlapped at both 
ends by the more massive ridges of fresher drift that belong to 
this formation, and it in turn overlaps with its fresher material 
the thin and much eroded drift of the earlier trains. It is here 
correlated with a well marked drift sheet of northern Illinois 
traced by Mr. Leverett, from the Wisconsin line southwestward 
down the Rock river valley to the Mississippi and identified by 
him with the upper till of the old drift sheet described in Iowa 
by Mr. McG-ee. Some features, however, of this morainic belt, 
which marks the periphery of this bowlder train suggest that 
it may be correlated with the still later drift sheet bounded in 
northeastern Illinois by the Shelbyville moraine. In this case 
we have within these limits a train formed by two successive 
episodes of glacial advance extending in this area along the 
same lines and therefore indistinguishable in their effect upon 
the drift material. 
The latest bowlder fan belongs to Green Bay lobe of the last 
ice sheet and coincides both in extent and in direction with the 
lines of drift movement indicated by the glacial markings and 
the till accumulations of that formation. Its bounds are well 
defined, being marked by the great abundance of quartzite ma¬ 
terial in its trains. Its breadth increases from eight miles on 
the south margin of the ledge area to seventeen miles on the 
outer border of the Kettle moraine. Its area is about 360 square 
miles. Its surface material aggregates about 35,000 cords, and 
the relative proportions of local material exposed in drift sec¬ 
tions varies from 15 per cent, in railway cuts half a mile south 
of the Hubbellton ledges to one three-hundredth in sections on 
the outer slope of the Kettle moraine. The amount of material 
which is included within the body of the latest drift is estimated 
from observations made in sections over all parts of the area to 
show a removal of from fifty to seventy-five feet of rock from 
the surface of the exposed ledges. 
Beloit , Wis. 
