474 GEOLOGY OF CENTRAL WASHINGTON TERRITORY. 
water destroys growing crops. Wheat does not fill after being submerged. Behind this river- 
belt, the upland is well watered and fertile. The gravelly country back of Vancouver is speedily 
exhausted, two crops of wheat being as much as it will produce to advantage. The Indians raise 
excellent potatoes on the Yahkohtl and Chalacha prairies; and wheat would undoubtedly thrive 
there; but they are subject to summer frosts. 
The timber upon the lower lands of the Columbia. is chiefly cotton-wood; on the smaller streams, 
vine-maple and alder » while the upland is covered with the usual growth of the coast region of 
Oregon—fir, spruce, and, towards the mountains, arbor vitee. This forest is almost entirely of 
secondary growth, and is deadened over a vast tract by the fires which run through the country. 
The fires would seem to add but little to the fertility of the soil, as the trees when consumed have 
hardly any ashes, and the roots burning out beneath the soil destroys all vegetable decomposition. 
The succession of forest which so universally takes place in the Atlantic States does not occur 
here, the few deciduous trees of the country being such as grow only upon the water-courses. As 
a consequence, the firs almost invariably spring up again when burnt off. The underbrush, con- 
sisting of hazel, spiraea, &c., is usually dense. In some isolated tracts the primitive forest remains, 
and the body of timber is heavy, though much less so than upon the Cascades south of the 
Columbia. 
The first rock in place encountered after leaving Vancouver was near the Yahkohtl fork of the 
Cathlapoot’l river, and was a hard and dark-green hornblende, without noticeable strike or inclina- 
tion to the beds. This rock forms the canon of the stream and prevails to the Cathlapoot’] itself. 
Boulders of trachyte accompanied the sand and gravel in the Yahkohtl, but not in such quantity 
or variety as in the main fork which heads in Mt. St. Helens. The divide between the latter 
and the Columbia is about 1,800 feet in height, presenting a steep and almost precipitous face to 
the north. The hornblende rock is said to extend down the Cathlapoot’l to within a few miles of 
its mouth. Sandstone of volcanic origin appeared in large masses on the borders of the river, and 
probably occurs in place at no great distance. The boulders in its bed are chiefly trachyte of 
different shades, and basalt, varying from scoriaceous to compact, and very fine grained. There 
is but little valley on its upper waters, and that of no value, as the soil consists almost entirely 
of the detritus of these rocks. As might be supposed from its draining the southern and eastern 
slopes of Mt. St. Helens, the river bears evidence of its great volume during the melting of the 
snows. 
On the north bank of the Cathlapoot’l, and about four miles below the mouth of the Noompt- 
namie, we crossed a field of lava apparently formed by a stream from St. Helens. Its surface 
was everywhere broken into mounds, or gigantic bubbles, produced apparently by the expansion 
of contained gases, or perhaps the moisture of the soil over which it had flowed. These mounds, 
which were generally of an ovoid shape, varied in size from six or eight feet to a hundred in 
length, and in some cases rose to twenty and thirty feet in height. Their tops were broken into 
fissures, the principal corresponding with the longer axis. The direction of this was not uniform, 
but in the larger seemed to agree with what is supposed to have been the course of the current. 
The edges of the fissures were perfectly sharp, indicating that the lava had at least partially 
cooled before fracture; but, on the other hand, quantities of loose clinkers lay upon the sides of 
the mounds, and small waves produced by the progression of the lava were visible, which seemed 
to diverge from them. Flat slabs, resembling flags, two or three feet long and a couple of inches 
thick, also occurred. The surface was vessicular, the inferior portions as seen through the fissures 
more compact; its depth was not determined. 'The field had been covered with forest, which, 
like much of that on the route, had been burnt over. Unfortunately, time did not admit of a 
visit to the river to examine the termination of the stream, nor yet to the bluffs on the left, to 
ascertain if the lava underlaid them. These bluffs, extending in a line with the river for some 
distance, were in places three or four hundred feet in height, composed of sand and boulders of 
trachyte. The width of this field was about one-third of a mile. A bed of fine volcanic ashes 
