January 38, 18«7.J 



SCIENCE, 



83 



corroborated by many other circumstances which 

 need not be enlarged upon here. No geologist 

 who has visited the locality has ever doubted, so 

 far as I know, that this is, in general form, the 

 true explanation. The only question which arises 

 is about the nature of the obstacle which has 

 dammed the river. Dr. Newberry, who visited 

 the place in 1855 in connection with the Pacific 

 railroad surveys, suggested that it might be due 

 to the slipping of the bank of the river into mid- 

 stream at the Cascades, thus throwing the current 

 upon the southern bank. This idea has diffused 

 itself among the people of the neighborhood, and 

 is frequently spoken of as the vera causa. In 

 support of this view, reference is frequently made 

 to the second fact ; viz., the slow lateral creeping 

 of the railroad-track on the southern bank of the 

 river. 



Desiring to see these phenomena, which seemed 

 to promise much instruction, I made a visit to 

 the place, and devoted a couple of days to their 

 examination. As regards the creeping of the 

 railroad-track, the explanation is patent as soon as 

 the spot is visited. The place is situated on the 

 south bank, about a mile below the cataract. The 

 materials which are creeping are felspathic sands, 

 deposited by the river itself in irregular strata, 

 and now undergoing rapid decomposition and 

 kaolinization. The products of decomposition be- 

 come a smooth slimy clay ; and having a rather 

 steep front toward the river, which is here a swift 

 and powerful torrent, the slope of the bank is a 

 little too steep for stability. The materials, being 

 of a somewhat unctuous character, flow easily 

 with a slow glacier-like motion. The phenomenon, 

 however, is a local one, limited to a stretch of 

 only a few hundred yards, and does not occur 

 anywhere else in the neighborhood, so far as I am 

 aware. The bed-rock beneath it is disclosed, and 

 there is no indication that it participates at all in 

 the motion : on the contrary, the indications are 

 very plain that it does not. It also became evi- 

 dent, that, whatever might be the origin of the 

 obstruction which has backed up the Columbia 

 River for nearly fifty miles, this particular phe- 

 nomenon has had nothing whatever to do with it ; 

 though possibly it may be, and probably is, a re- 

 mote consequence of the obstruction. It certainly 

 is not the cause. 



In looking upon the north bank for indications 

 of a slide which could have precipitated any ob- 

 struction across the channel, I vs^as unable to find 

 any. On the contrary, the more carefully the 

 ground was studied, the more difficult it seemed 

 to reconcile this supposition with the facts ; for 

 there is no steep elevated ground, from which an 

 obstructing mass could have slidden, nearer than 



three miles. The river-valley is here very wide, 

 and north of the river lies its ancient flood-plain, 

 which consists of ancient lavas and conglomerates 

 in heavy masses, planed to an approximate rough 

 level, with patches of river-gravel and sands scat- 

 tered over it. The study of this old flood-plain 

 disclosed facts which seemed to furnish a much 

 more satisfactory solution of the problem. 



Beginning at a point about a mile above the 

 cataract, this flood-plain is seen to ascend as we 

 go down stream. If the proper stand-points are 

 selected, this slope in the wrong direction is con- 

 spicuous to the unaided eye. But we need not 

 rely upon such a means of verifying the fact, for 

 the relation of the river, as it now runs, to the 

 older flood -plain, tells the story with emphasis. A 

 mile above the rapid the old flood-plain is no more 

 than thirty feet above the water ; a mile below 

 the rapid it is about two hundred feet above it ; 

 while the fall of the river itself in that interval 

 is not more than forty feet. The inference seems 

 decisive. There has been an uplift of the entire 

 platform athwart the river-valley in the shape of 

 a very flat anticlinal arch. The width or span of 

 this arch is about five and a half miles, and the 

 eastern branch of the flexure is steeper than the 

 western. The displacement is not recent in a 

 historical sense, but it is probably post-glacial. 



The effects of such an obstacle would be mani- 

 fold. Not only would it dam the river, but it 

 would set up below the cataract an action which 

 it is important to consider. A great river, thus 

 obstructed, at once attacks the obstacle with im- 

 mense power. And the more pronounced the 

 obstacle, the more vigorous the attack. The Co- 

 lumbia has already cut through it a low, inner 

 gorge somewhat similar to that of the Niagara 

 River below the falls. The rapid at the locks is 

 steadily receding, and, if no further displacement 

 occurs, it will probably require not more than a 

 century or two for the river to have cleared a pas- 

 sage deep enough to drain the slack-water reach 

 above. The work of cutting a passage through 

 the obstruction five and a half miles in length is 

 nearly complete. That the dam was once higher 

 than now, is also to be inferred. Year by year it 

 is getting lower. The effect of the obstacle upon 

 the slack water above it is also plain. The flow^ 

 of the water being retarded, it drops its sediment, 

 and the river-bed is gradually built up. Thus the 

 trees which grew along the flood-plain before the 

 upheaval were not only submerged, but were 

 buried in sand and gravel. When the dam was 

 higher, they were more deeply buried than now. 

 As the dam is gradually cut down, the trees are 

 slowly exhumed again. But it is well known 

 that trees submerged in fresh water and buried 



