80 



Referred to sea level, the southern or downstream end of the upper 

 terrace is about 20 feet higher than the northern, or nj^stream end. That 

 is, in a distance of a little more tlian two miles tlie terrace level rises 

 20 feet liijilier above sea level, while the surface of the water in the stream 

 has a fall of about 37 feet in the same distance, makinj; a total differen- 

 tial level between the surface of the terrace and the surface of the water 

 of about r>7 feet. 



Tile terraces of the lower level are from 2.1 to ?,~t fcHit lower than those 

 of tlie upper level and are fotind only in the lower portion of tlie canyon- 

 like part of tlie valley ; their width is about the same as that of the upper 

 terraces, averaging iierhaps 2.1 or 80 feet, with a maximum of from .10 to 

 ('0 feet. The height of stirface of tliis lower series above tlie stream also 

 increa.ses in the downstream direction, but at a much smaller rate than in 

 the case of the upper terraces ; in a total distance of about two-thirds of 

 a mile the difference in elevation is about feet. The fall of the stream 

 is, in the same distance, a little more than G feet, whicli leaves the surface 

 of the lower series of terraces with a very slight gradient in the down- 

 stream direction, when referred to sea level as datum. 



Considering, then, the upper terrace level, the lower terrace level, and 

 the present gradient of the stream in their relations to eacli other, the 

 lower terrace level can be represented by a nearly horiznntal line drawn 

 a little lower than mi<lway between two other straight lines wliich diverge 

 in the downstream direction ; the upper representing the surface of the 

 upper terrace le^el, and the lower the present gradient of the stream. 



CONCLT'SIONS. 

 Tin- causes whlcli operated to make tlie c(mditions resulting in the 

 terraces aliove descrilted may, n<> doiilit, be iiiclndid for the most iiart in 

 the following: 



1. Variations in ttH> amimiit of stMlinieiit carried by the streams. 



2. Variations in the amount of water carried liy the streams. 



3. Variations in gradient due to — 



(a) IMastroiihism ; 



(111 Dams (if ice and glacial debris nuin' nr less coniiilete. 

 n'sulting in ponds, river hikes, ete. 

 Wiiile it is imt imssible t<> s;iy pusitivcl.N Jnsl what sli.ire eiicii of these 

 causes may Inive had in the formation of eacli one of these (erraei's. the 

 following partial e.vplanations seem to lie .justitied: 



