96 E. Desor on the Drift of Lake Superior. 
o rule obtains as to the composition of the drift sand and 
gravel, either in reference to the size or the mineralogical char 
acter of the materials. ee 
Layers of fine sand alternate in every possible way with layers 
of pebbles—sometimes by a gradual transition, at others rather 
abruptly. ‘The pebbles themselves are composed of all kinds of 
stone—some from the immediate neighborhood, ,others from 
places more remote. They are generally rounded and smoothed, 
showing that they must have undergone a prolonged and violent 
motion, such as could have taken place only in the water. The 
drift-sand and gravel, like that of the clay, is best ascertained 
along the shore of the lake. There seems to be a sort of antag- 
onisia as to the relative thickness of both deposits between the 
eastern and western portions of the lake shore. Whilst the clay 
Seems to assume its greatest thickness west of Keweenaw Point, 
cliff to the southeast, generally some miles distant from the lake 
shore ; until it reaches jt again at Pointe Iroquois, where it riseS 
almost to the same height—345 feet; thence it sinks gradually 
towards the Saut. As a further peculiarity of the drift-sand and 
gravel deposits we would mention their irregular-and undulating — 
surface, especially where they cover wide tracts of country: 4 
