Wcoldridge ofi the (River =Lake Syetem of W. Mich. 145 
common opinion has been that the subsidence followed glacia- 
tion,and was a phenomenon of the Champlain epoch rather than 
the glaciation. Under the views here set forth the beaches 
which remain date from the commencement of the decline of 
the glacier. 
Croll, who has so ably speculated on the causes of contin- 
ental glaciation, conceived the icy load as heaped above the 
former level of the continent. . He viewed the crust as too 
rigid to b^ depressed by the weight. A polar ice-protuberance 
of 5,000 feet, and covering all the north temperate lands, would 
shift the earth's centre of gravity northward to a certain extent. 
The oceans would as a consequence, flow northward to restore 
the proper figure of the earth, and all northern lands would 
suffer inundation. This reasoning becomes nugatory in the 
face of much evidence that the earth's crust has many times 
yielded to the pressure of accumulated sea-sediments, and would 
much more yield to the weight of a continental glacier. 
THE RIVER-LAKE SYSTEM OF WESTERN MICHIGAN. 
l!Y C, W. WOOLDUIDGE, B. S., M. D. 
The attention of geologists does not seem to have been di- 
rected to the peculiar system of river-lakes found along the 
eastern border of lake Michigan, to the degree \vhich their im- 
portance merits.' 
The map accompanying this article represents a portion of 
the lake Michigan border, along the northern part of Muske- 
gon county, Mich. A glance at any good map of the state will 
show that the system of lakes occupying the lower valleys of 
streams flowing into lake Michigan, which the region depicted 
in this sketch so well illustrates, continues throughout the whole 
length of the east shore of lake Michigan, from Grand Traverse 
bay on the north to the St. Joseph river on the south. 
A careful study of the vicinity of White lake, shown in the 
1 These features were pointed out and mapped by Alexander Winchel 
in an article in Harper's Magazine for July, 1871, p. 2S4. [Ed.] 
