THE NORTHERN PACIFIC ROUTE. 163 
At Fishtrap there are a number of small hills on both sides of the 
track which appear, to one familiar with glacial topography, to be of 
glacial origin. When examined closely they are 
found to be composed of light-colored clay or shale 
which is very different from the material deposited 
by ice. The peculiar hummocky form of the hills is 
due to the softness and fineness of the material composing them and 
to the peculiarities of erosion in a semiarid climate. Few if any 
watercourses are developed in the hills, hence they have no regular 
pattern or arrangement. ‘The rains are infrequent, only a few gullies 
are established, and the development of such gullies tends to produce 
isolated conical mounds rather than low continuous ridges, such as 
would be produced in similar material in more humid regions. é 
As the material composing these hills is fine and evenly bedded, 
it was probably deposited in a body of standing water, and as its 
age, so far as the evidence has been obtained, corresponds in a gen- 
eral way to that of similar beds (Ellensburg formation) in the Yakima 
Valley, it is considered to be a part of that formation. The bulk of 
the sediment deposited in this great lake was dropped near shore in 
the vicinity of the Cascade Mountains, and only the finer material 
was carried as far east as Fishtrap. This was deposited over the 
basalt in a thin sheet, which has been largely removed, leaving iso- 
lated outliers like those described above.’ 
Near milepost 123 there is some rough country that shows on a 
small scale the effect of erosion on the sheets of basalt. In a more 
humid region most of the sharp edges of the tables would be rounded 
off and the slopes would be gentle and regular, but in a semiarid 
country each remnant of a lava sheet or other hard bed of rock stands 
up sharp and distinct as steps on the hillside or as isolated tables or 
mesas on asmallscale. Thus the sheets-of lava were not swept away 
Fishtrap. 
Elevation 2,282 feet. 
St. Paul 1,536 miles. . 
whether these bowlders were brought di- 
‘Although there is litile doubt about 
the origin of the Fishtrap Hills, there 1s 
considerable uncertainty in the minds of 
geologists as to whether there has ever 
been an incursion of the northern glaciers 
into this region. The fact which leads to 
the belief that ice once occupi 
country is the presence, far southwest of 
Spokane, of bowlders of granite and quart- 
zite 12 to 20 inches in diameter. These 
bowlders are not numerous, but occasion- 
ally the traveler, if his sight is sufficiently 
tch glimpses of them, even 
Generally 
pation of the country by ice, but it has 
not yet been satisfactorily de 
rectly by the glacier and were dropped 
from its moving mass, whether they were 
floated along on cakes of ice in a large 
lake, or whether they were simply washed 
out over this p 
it was in the vicinity of Spokane, If the 
bowlders here were as numerous an) 
large as the bowlders in North Dakota west 
of Missouri River there would probably 
be no question as to their glacial trans- 
portation, but in the State of Washington 
that some doubt naturally arises as to 
whether moving ice was the vehicle by 
which they were transported to their pres- 
i laces. 
ent resting p. 
