QUATERNARY AGE. — CHAMPLAIN PERIOD. 547 



become flooded in modern high freshets ; in other words, the flood- 

 grounds ; e/*, e'f 1 , are the flood-grounds of the river during the great 

 Champlaiu floods (or what is left of them) ; and the intermediate ter- 

 race-plains are other levels, formed either during the rise of the flood, 

 the water while on the increase flowing long, it may be, at certain lev- 

 els ; or during the decline, which also may have taken place by stages, 

 and have been long in progress. Part may be under-water levels ; 

 for great streams and lakes, or lake-borders, often have shoals at two 

 or three levels ; and part may have been occasioned by the contribu- 

 tions of side valleys, and unequal resistance to wear. 



The stratified beds consist either of clay, earth, sand, gravel, or 

 gravel with a large admixture of cobble-stones or bowlders. Beds of 

 these kinds may alternate with one another, and occur at various in- 

 tervals in the deposits ; but along the larger river valleys, clay deposits 

 are most common toward the bottom, and pebble and cobble-stone 

 beds toward the top. As in other cases, the rate of flow in the waters 

 influenced the nature of the deposit as explained on page 654, and 

 hence the kind of material is an indication of the rate of flow during 

 the deposition. The bed that consists of clay at one place may thence 

 be of sand a few rods off, or have at times interlaminations of sand ; 

 and the high-terrace formation, chiefly composed of sand-beds, may be, 

 and often is, topped by the very coarsest of a river valley because of 

 the violence of the floods during their later depositions. The clay de- 

 posits are most extensive about lakes, or where the rivers were wid- 

 ened into lakes ; and they have usually the thin lamination of ordinary 

 river deposits. Owing to their great extent over the region north of 

 Lake Erie, the beds there have been designated by Logan the Erie 

 clays. These clay deposits may rise but a few feet above modern low- 

 water mark in one part of a valley, and a hundred feet or more in 

 another part ; this depending on the shorter or longer continuance of 

 the period of quiet waters, and other conditions. Occasionally such 

 clay beds contain isolated bowlders, a ton, more or less, in weight, and 

 in this, as well as their being overlaid in places by coarser stratified 

 drift, they show that they are true Drift deposits ; for only overhang- 

 ing or floating ice could have dropped to their places such masses of 

 rock. The lower beds of the clay deposits in the region of the Great 

 Lakes have sometimes, at or toward the top, local beds or patches of 

 vegetable debris — as stems, roots, logs, and mosses — blackened but 

 not carbonized, as noticed by Newberry, near Cleveland, Ohio, and 

 earlier by Logan, near the Grand Sable and Goulais Rivers. Since 

 the material earliest deposited from the melting glacier would have 

 been the heavier scratched bowlders, stones, and gravel of its under 

 portion, the very bottom of the valley Drift would naturally be of this 



