270 Tin Aiini'inin ( tcoliKjist . November, 18!ll 
ri'uioii is tluTfr«tn' peculiarly lilted to llie iiKiuirv in hand. If 
we follow nortliwanl alonji the axis of the eentval ice-loi)e in 
Illinois. we eneounter. within aViout one hundred miles of tJie drift 
border, a lii'oad ridue of drift, identilialile as a marginal moraine: 
and farther to tlu' northward, similar ridges reiiresenting lati>r 
staijes of <jlaeiation. The first eiijht of these bear common 
ehararteristics. all sioiiiijcant of the attitmle of the surface at the 
times thev were formed. Thev are all l)roa(l swells <»f t>;entle slope 
and smooth, thoujrh unchUating. contours with the exci'ptioii of a 
few local departures. Thev ;in' not puslie(| into routjh indente(l 
ridges, as is the fashion with terminal moraines forced up by 
vigorous glacial action. They apjjcar rather to be the suV)mar- 
ginal accumulations of a sheet of ice cret'i)ing gently down ui)on 
a plain of slight inclination. This interpretation, which in itself 
might be ([uestioned. is supported by the significant fact that on 
the outer side of these moraines there are fi'inging l>elts of silt 
produced by the waters that crept over them while presse<l on the 
inner side by the ice. These bordering silt-sheets terminate in 
and oil the moraines and reach out to varying dist:inces upon the 
plain to the southward. 
It would ai)pear. therefore, that we have in these i)hiMioniena 
evidences that cannot l)e gainsai<l. that during the several suc- 
cessive stages that these moraines represent the attitude of the 
country was low, and that tlu' drainage was more slack than at 
the present time. 
IV. Tilt Riifjijid R'nUj<x mill (irincl ^Ijiruiis uf tin Lntir 
Mom i III s. The preceding phenomena represent the earlier and 
much the longer portion of the glacial i)eriod. Hut when, in 
coming northward along the Illinois river, we reach the inoraine^ 
which crosses at .Marseilles, and when, in ascending the Wabash 
river, we reach the nioi'aiuc which crosses at ,Vttica. we lind a 
notal)le change in the phenomena. The moraine is not only mon* 
rough in contour and rugged in constitution but is accompanied by 
much more al)uudaut evidencesof wash and assortment in the form 
of gravel hills and gravel tracts. On the outside of the moraine, 
instead of aprons of silt indicating (piiet overwash. there are 
aprons of gravi-l indicating more vigorous overwash. These fring- 
ing gravel tracts gather themselves somewhat promptly into the 
leadiui; rivi-i' valleys and Mow down these in the trenches now oc- 
cupied liy these streams, which aic cut into the older sheets of 
