26 THE ORIGIN OF ALKALI 



so the area was covered with thick layers of sand and 

 shale, hut the sea does not seem to have continued without 

 interruption. Arid conditions seem to have again pre- 

 vailed and the sea was reduced so that isolated portions 

 became brackish and from these isolated waters gypsum 

 and other salts were precipitated. 



"At the end of the Montana series the sea seems to 

 have again entirely disappeared and the area was subject 

 to erosion. 



"In the beginning of Tertiary times the section was 



* 



* 4 





I 



'} S. ir,. 





Fig. 2. Mancos Shale Hill. Soil from this Formation 

 is High in Alkali. 



again covered with inland seas over much the same area 

 as that occupied by the upper Cretaceous. The lower 

 portion of these Tertiary deposits consisted of yellow and 

 reddish-yellow sandy clays with regularly bedded sand- 

 stones, with some conglomerates near the base, over which 

 were deposited thin beds of light-colored sandstones asso- 

 ciated over much of the area, especially in Utah, with 

 rhyolitic ash beds and fresh-water deposits. In some 

 places the ashes show distinct stratification as though they 



