Great Lake Basins of the St. Lawrence. 269 
bed of the lake, and with deep inlets joining it from the 
north, north-east, north-east by east, south and south-west 
sides, and the whole connected towards the south-west end 
with the deeper parts of the lake beyond. The descent is 
generally so abrupt from the shallower parts of the lake on 
either side to the depths of this depression and its inlets as 
to convey the idea of escarpments or bold cliffs almost sur- 
rounding the depression. The Helderberg anticlinal 
separates it from the old subaqueous river channel. On 
the other hand, Little Traverse Bay—another fracture in 
the Michigan coast—which has 150 to 230 feet of water 
everywhere within half a mile of its shores, may be said to 
lie about due east and west. It is important to thus note 
the varying directions of the forces which have given rise 
to these different depressions or great fractures. 
The southern half of Lake Michigan has a generally uni- 
form appearance. Its coasts are not indented with deep 
bays, but preserve an outline somewhat straight at the sides 
and curved at the southern end; the waters, though shal_ 
lower towards this southern end, have on the eastern and 
western sides a gradually increasing depth towards the cen- 
tral plateau of the lake; the lake floor, excepting the anti- 
clinal or warp in the strata between Milwaukee and Grand 
Haven, is comparatively level and somewhat, but not alto- 
gether, free from abrupt depressions; and whilst the lake 
floor in the northern half of the lake is frequently rocky, it 
is in the southern half almost entirely overlaid with clay or 
sand. ‘These deposits of sand are much more general along 
the whole western and southern than on the eastern coasts, 
indicating at the time of deposition stronger currents to- 
wards these sides. In fact, the southern end of the laixe in 
its general contour and depths, and in the character of its 
floor, corroborates the view that whilst an outlet to the Mis- 
sissippi valley from the united lakes existed here, it also for 
a considerable time was an outlet of the present lake before 
its waters had receded to their present limits. 
The section of country to the south and west of the 
southern end of the lake is largely prairie, that part imme- 
