XI INTHODUCTIUN. 



the other led south-west past lludsonvillc to enlcr the lake at Zee- 

 land. Great gravelly deltas were fornud by e:icli Vjrnti'.-lj of the 

 old outlet at the places where they entered the lake. Much of Al- 

 lendale Township, Ottawa County, is in the (Icltii of the north 

 branch, while Zeeland stands on the delta of the south branch. As 

 these gravelly deposits are now 60 or 70 feet above I^ake Michigan, 

 it is certain that the level of Lake Chicago was about that height 

 above the present lake. Later it dropped to lower levels, and the 

 outlet of Lake Saginaw along (Jrand River Valley became corre- 

 spondingly deepened. 



•'The variations in the drift material gave rise to several classes 

 of soil ranging from heavy clay through loamy clay, clayey loam, 

 sand, and gravel, up to coarse cobble. It is usual, however, to find 

 in gravelly places a surticient amount of fine earthy material to af- 

 ford asuitable matrix for plant roots. 



"Perhaps the coarsest deposit within the Grand Rapids district is 

 that in the old lake outlet. Between the City and Grandville the 

 current ot water removed the line material to such a degree that 

 the soil is very stony. In the western part of Grand Rapids and for 

 some miles above the City large numbers of boulders were present 

 in this outlet before the residents made use of them in building. 

 The soil among the boulders was, however, not too coarse for 

 plants to thrive. This same lake outlet carries also some of the 

 most extensive swampy tracts in the district; the Zeeland Swamp 

 south-west of Hudsonville, the Cedar Swamp west of Jenison, 

 and the Burton Avenue Swamp south-vrest of South Grand Rapids, 

 being illustrations. But this swampy condition is due to subse- 

 quent plant growth in the part of the channel having exceptionally 

 flat bottoms, rather than to any deposit made by the outlet. It is 

 found that sand and gravel deposited by the lake outlet underlie all 

 the swamps at a depth of only a few feet. 



"The strip of gravelly sand which extends from the bend of Grand 

 River near Plainfield southward along the east side of Grand Riv- 

 er throtigh Grand Ra]>ids and to Carlisle, being in the line of a 



