﻿194 ELEVATED RIVER'S BANK. July, 



hard when barriers of ice, during the high spring 

 floods, often raise the river thirty feet above its 

 ordinary level. Then the frozen earth resists the 

 action of the water as a rock would do, and the 

 surface yields only in proportion as it thaws, which 

 is slowly, since the water loaded with ice is kept 

 down to the freezing point. 



I observed that the bank of the river was gene- 

 rally higher than the land behind it, by at least the 

 thickness of the diluvial capping, and sometimes 

 by a part of the sand or clay of the tertiary beds, 

 and that the narrow elevated bank extended in the 

 same form along the principal affluents, a marked 

 instance of which occurs on the south side of Great 

 Bear River. In consequence of this configuration of 

 the surface, the spring floods of melting snow accu- 

 mulate, and at length make their escape through 

 gullies, contributing further to the ruin of the bank, 

 and giving it a broken and hilly outline when seen 

 from the river. Landslij^s are of common occur- 

 rence, and are occasioned by pressure of water 

 collecting in fissures produced by the partial sub- 

 sidence of the clifl".* 



* Similar tertiary coal formations occur on the flanks of 

 the Rocky [Mountains ; the most southerly one of which I 

 have any account, being in the Eaton Pass, in latitude 37° 15' 

 N., longitude 104° 35' W., and upwards of seven thousand feet 

 above the level of the sea. Leaves of dicotyledonous trees, 

 obtained in these beds by Lieutenant Abert in 1847, are figured 



