VOLCA^'IC DISTURBANCES 367 



FORMATION OF SNAKE RIVER 



Eeasons for believiiio- Snake Eiver to be a very modern stream are pre- 

 sented in another connection. If the lava Avhich filled the gorge rmming 

 east of Pocatello represents the channel of a south-flowing master-stream, 

 into Avliicli once gatliorcd all the headwater branches of the Snake liiver, 

 tlie incursion of molten rock in such bulk as is plainly manifested at 

 once effectually blocked all further southward movement of the waters 

 oT these head streams Ijoth tlirough this channel and its valley. By avhv 

 of contrast the Eio J\Iora, wlien, owing to the great depth of its canyon, 

 the lava was unable to completely fill it, excavated a new channel along- 

 side of the old one. That the Aoluminous waters of the Snake ~R[\ev 

 wlien turned out suddenly on to the arid Idaho plains should form a 

 notable river rather than a lake is due to a number of peculiar circum- 

 stances. Possibly at first ephemeral lakes were formed which, as their 

 low rims were successively pierced by overfloAv waters, were quickly 

 drained^ and only a stream persisted. Various lava flows may have de- 

 termined the dams for the impounded waters. Today the locations of 

 these dams may be indicated by the positions of the different "falls" 

 which characterize the course of this river. 



P>y all expectation the Snake Eiver should be a typical example of an 

 antecedent stream. In arid regions^ however, as Davis well observes,^^' 

 antecedent rivers persisting from a previous cycle against the deforma- 

 tions I)y which the new cycle is introduced must be rare, because such 

 rivers should be large^ and large rivers are iiere unusual. In so far as the 

 course of the stream under consideration is determined by the slopes of 

 its new surface^ the Snake Eiver is a consequent stream; but not in the 

 usual sense of the term, for general deformation does not enter into the 

 problem at all. This great waterway really belongs to a new class by 

 itself. 



Among streams generally the Snake Eiver presents a rather unique 

 genesis- It is iioav essentially a typically through-flowing stream of the 

 desert, with extra! imital headA\'aters. Without taking any part in tlie 

 general sculpturuig of the landscape of the region through which it 

 passes, it is a river seemingly out of place. It is not a stream which 

 merely lengthens or shortens ^yit]l the oscillation of the ocean's strand- 

 line. It is not a stream that is formed of several streams united end to 

 cjid. It is not dependent for its existence on the run-off of storm waters 

 from the surface of a warpijig area. It is not a stream that has held its 

 own from a former cycle. It appears to have burst full grown from its 



lo.lonriial ol: Geology, vol, xiii, ISUo, p. 381 



