100 
EIGHTH REPORT. 
while inland lakes and streams are supplied very largely through the 
drainage from their watersheds both surface and underground. 
Of the Great Lakes, Superior has much softer water than Michigan, 
Huron and Erie, there being less than half the amounts of calcium and 
magnesium carbonates in its waters. Available analyses show for Lake 
Superior waters about forty parts per million of carbonates of calcium 
and magnesium, for Lake Michigan waters eighty to ninety-two parts, 
while those of inland surface waters of the Southern Peninsula run 
from 100 up to 300 parts per million. (See Lane Water Supply Paper, 
U. S. Geological Survey No. 31, also Annual Report of State Geologist 
for 1903, pp. 112-161.) This variation is readily accounted for by the 
geological conditions, limestone or other rock formations which give 
hardness to percolating water being poorly represented within the Lake 
Superior watershed compared with their occurrence within the water¬ 
sheds of the three other lakes. The glacial deposits also being composed 
largely of material of local derivation contain much less calcareous 
material within the Lake Superior watershed. Lake Superior is not 
only softer than the other Great Lakes, hut its waters remain cooler 
through the summer months so that it is the most palatable of all 
the waters. The cities on its borders, therefore, have an unexcelled 
water supply so far as geological and geographical conditions are con¬ 
cerned. The waters of the other Great Lakes are also suitable for 
boiler use and are largely drawn upon to supply commercial and manu¬ 
facturing needs. 
The hardness of the inland lakes and streams like that of the under¬ 
ground waters is found to be generally above 140 parts per million, 
or the limit considered suitable for good boiler water, though there 
are a few notable exceptions where lakes have very small affluents. 
Turbidity. The Michigan streams as a rule carry so little matter in 
suspension that so far as sediment is concerned they appear well 
adapted for domestic use and all other purposes where clear water is 
desired. The small amount of sediment carried by them is due to the 
fact that much of their supply comes through underground instead of 
surface runoff, the drift deposits being so porous that a large part of 
the rainfall is directly absorbed and then fed slowly to the streams by 
seepage. Since the slopes have been cleared and cultivated, and con¬ 
ditions made more favorable for surface runoff the streams are more 
frequently turbid than they were in the natural state of the country, 
but even now the condition of Michigan streams in this respect is 
better than any of the neighboring states. In some cases turbidity 
is caused by winds and the currents Avhich they produce. The lake 
currents bring sand to the outlet of Lake Huron and this is carried 
through the St. Clair River to form the delta at the north edge of 
Lake St. Clair. Port Huron and other cities drawing supplies from 
St. Clair River thus have a somewhat turbid supply. At the head of 
Saginaw Bay the water is so shallow that storms disturb the sand and 
render it turbid for some miles from the shore hut this condition is only 
occasional and is therefore of slight detriment to the Bay City supply. 
The waters of the lakes are very clear except in the shallows where 
waves and currents stir up the sand. The disturbing effect of waves on 
the shores has made it necessary at several points to extend intake pipes 
out into deep water. 
