212 The American Geologist. October, 1904. 
Again, one to two miles south of Tenino, Grand Mound 
prairie, whose eastern end is crossed by the railway, and which 
extends thence seven miles westward, takes its name from the 
same moraine mounds. 
On the more western railway, running from Olympia 
southwest to Gate, and thence westerly to Gray's harbor 
these mounds are seen in great abundance on a prairie two or 
three miles in diameter at the distance of three to five miles 
northeast of Gate. Extensive gravel excavations, for ballasting 
the railway, have been made in the central part of this prairie, 
near Mima station. Several of the mounds, 2 tO' 3 feet high, 
half cut away, are seen to be through their entire thickness of 
the same black color as the surface soil, which elsewhere has a 
depth of only 4 to 6 inches ; but no difference is observable in 
the coarseness of the gravel forming the mounds and the in- 
tervening ground. Pebbles and cobbles from 2 to 4 or 6 inches 
in diameter are plentiful in the mounds, on the general surface 
between them, and for several feet downward. 
At Gate (also called Gate City) the same gravel surface is 
much mounded and ridged, inclosing occasional bowl-shaped 
depressions 2 to 5 feet deep. In a miniature degree, the con- 
tour at Gate resembles that of a typical tract of kames. which 
usually consist of such coarse gravel ; but on the Mima prairie 
many hundreds of round mounds, 2 to 5 feet high, occur sepa- 
rate from each other, and are often very thickly grouped to- 
gether. 
The gradation of forms from round mounds to interlock- 
ing ridges and mounds, like small reticulated kames, debars 
the reference to aboriginal mound building, or to mounds of 
any burrowing animals, which at the first view are suggested 
bv these very unusual drift deposits. Their true explanation 
has been well stated by Rogers, referring them to accumula- 
tion in little hollows of the finally very thin margin of the ice- 
fields when they at last melted back from this outermost tract 
or terminal moraine belt. 
Mr. John D. Henry, of Olympia, county surveyor of 
Thurston county, kindly supplied outlines and descriptive notes 
of the several "mound prairies" of that county, including 
Rocky, Grand Mound, and Mima prairies, already mentioned, 
and Tenalquot and Yclm prairies, lying farther east, on the 
