ARMS OF THE OCEAN 27 



had fallen into the inland sea and had been worked over 

 by the water. 



'The upper part of the Tertiary is composed of shaly 

 sandstone and arenaceous shale, and in some sections 

 thick beds of subbituminous coals. The shale and much 

 of the sandstone are gypsiferous and in many places con- 

 tain high percentages of sodium salts. 



''Near the close of the period the high evaporation 

 seems to have so reduced the sea that parts of it became 

 isolated lakes and from these brackish deposits were 

 precipitated the salts and gypsum in question. 



"The Green River formation- is composed essentially 

 of light-colored thinly laminated beds, characterized by 

 light-colored thin bedded shales. In appearance these 

 shales of the Green River formation are much like those 

 of the Mancos, especially some of the light-colored and 

 thinner beds. 



"The Green River shales weather into a series of 'bad 

 lands, and it is not an unusual thing to have a large area 

 entirely devoid of plants." 



Arms of the Ocean. Many soils have been formed by 

 deltas of streams deposited in the ocean. These sometimes 

 enclose portions of the ocean which may be shut off from 

 the main body of water. The inclosed salt water gradually 

 evaporates and leaves deposits of soluble salts or an alkali 

 condition in the soil. This may be either a surface ac- 

 cumulation that is comparatively easy to remove, or the 

 salts may extend to considerable depth and be very difficult 

 to handle. The type depends on the way in which the 

 soil was laid down and the nature of the area of inclosed 

 sea water. Subsequent deposits of soil may leave the 

 alkali at considerable depths. The alkali land of the 

 lower Nile Valley as well as the small alkali tract along 



