10 BULLETIN 141, TJ. S. DEPARTMENT OF AGRICULTURE. 
the deeper and quieter lake waters in positions more remote from the 
deltas of tributary streams and at some distance from shore-line 
borders. They usually rest either upon consolidated rock, upon 
glacial till, or upon the more sandy or gravelly materials which 
were sometimes deposited first as the ice retreated. 
Thus' the greater part of all of the glacial lake basins consists of 
marginal gravelly and sandy zones, of local sand plains and stream 
deltas, and of the heavier loam and clay deposits more remote from 
the sources of sedimentary supply. 
When the waters of the different glacial lakes were gradually 
withdrawn and the bottoms of these lakes exposed to form a land 
surface there were many minor inequalities of elevation which gave 
rise to wide differences in the drainage features of the lake basins. 
Areas lying between successive beaches frequently remained 
swampy. Shallow depressions in the broader lake plains still con- 
tained minor ponds and swamps. Only the higher lying areas and 
the more sloping surfaces became well drained immediately after the 
recession of the glacial lake. The broad level areas, occupied by the 
heavier clays and loams, together with all depressed areas within the 
glacial lake plains, remained swampy for a considerable period of 
time. In consequence large areas included within the glacial lake 
basins passed through a swampy stage which persisted in many 
instances until the occupation of the land by white settlers, and 
which has only been relieved to a partial extent through the installa- 
tion of artificial drainage. 
It is probable that water-loving grasses and the smaller forms of 
vegetation first occupied these swampj^ areas. It is certain that con- 
siderable areas of the swamp included within the glacial lake basins 
remained so poorly drained until within historic times that only a 
few species of trees found foothold within their limits, while in many 
instances considerable areas remained in the condition of treeless 
marshes or grass-grown swales. 
In other instances areas somewhat better drained eventually became 
covered with a heavy stand of ash, elm, soft maple, tamarack, and 
other water-loving trees. In all cases the swampy conditions gave 
rise to the formation of large amounts of humus in the surface soil 
and this has given a characteristic dark gray, brown, or black color to 
the surface layer of extensive areas of the glacial lake deposits in the 
north-central and northeastern States. These give rise to the soils of 
the Clyde series. Conditions of more perfect drainage gave rise to 
light-gray or yellow surface soils which are classed in other soil series 
than the Clyde. 
The different soils of the Clyde series, therefore, owe their origin 
to a complex series of events beginning with the glaciation of the 
northeastern and north-central States, followed bv the retreat of the 
