172 The America)! Geol(M/isf. March, 1S95 
end of the lake. Just as it lias actually (rolleeletl in enormous 
quantities at the south end oT lake Michigan. Hut the head 
of the St. Clair river opens just at the southern apex of lake 
Huron, and the result is that the drifting sand constantly 
passes into the river antl tends to build out spits across its 
head. This process has actually contracted the entrance to 
one-half the average width of the river below. The spit on 
the east side is well develo[)ed and its point has been turned 
down stream by the current of the river. The predominance 
of drift from the east shore has crowded the river over against 
its west blulf and filled in the old channel for a mile and a 
half on the east side. This crowding process has made the 
rapids at the head of the river. As the sand is swept into the 
opening it is caught by the current which sets in strongly at 
the start (four and a half miles per hour) and is carried down 
stream. Once in the current the sand is kept rolling along 
the bottom until lake St. Clair is reached. Here the river 
strikes still water, spreads out, and slackens its How. At this 
place, therefore, the sand comes to rest and the great delta of 
the clear river has gradually grown to immense proportions, 
and at a place altout 25 miles from lake Huron. IMie delta 
has filled in nearly a cpiarter of lake St. Clair, antl it covers 
nearly IW square miles. The average thickness of that part 
of the delta which has been built since the beginning of the 
eastward uplift, supposing the level of the lake at that time to 
have been about 35 feet lower, must be 25 to 80 feet. It there- 
fore probably contains not far from a cubic mile of sand, not 
counting submerged extensions, which would probably nearly 
double its area, but wdiich are mostly thinner and would not 
add greatly to the whole mass. 
It seems clear that the great eastward uplift did not occur 
until Niagara had consumed a lai-ge part, perhaps half, of the 
time which it has taken to cut the gorge back two miles. The 
rate of the recession of a cataract is liable to many irregular- 
ities. But if the rate for Niagara has been substantiall}'^ uni- 
form, then we might say that the St. Clair delta has been 
built in approximately the time that Niagara has been cut- 
ting back its last mile. Presumably the curr(>nt of the St. 
('lair river was stronger in the past, before drowning by tlie 
eastward uplift had jjrogressed so far as now. The power of 
