COLORS OF CONTINENTAL CLASTICS 623 



iron oxide, it would not produce red bricks, and it is not improb- 

 able that the lime would have the same effect in preventing the 

 formation of a red color with age. 



Alternation of Red Beds with Those of OtJier Colors. This is 

 a feature often found in older formations and has also been ob- 

 served in modern continental hydroclastics. Huntington (34:5(5^) has 

 described such deposits of pinkish or reddish sandy clays and sands 

 alternating with whitish or greenish clays from the uplifted and 

 dissected Pleistocenic deposits of the basin of Seyistan in eastern 

 Persia. These layers are well shown in cliffs from 400 to 600 feet 

 high, exposed by recent erosion. The red beds are continuous and, 

 while preserving their general aspect for many miles, they vary 

 greatly in detail. Wedging out layers of sand or even gravel occur, 

 slight erosion disconformities, occasional ripple marks, worm-casts 

 and rain-drops are not uncommon, and the uniform oxidation of 

 these beds indicates long exposure to the air under conditions of 

 aridity. This is further shown by the condition of the modern 

 delta deposits of the region, of which the subaerial part is well 

 drained and aerated and everywhere of a light brown color. On the 

 shores of the modern Lake of Seyistan, where the clayey beds are 

 saturated with water and subject to successive floodings, the brown 

 colors are replaced by light colored soils with black bands. The 

 margin of the present lake supports a dense growth of reeds and 

 the clay deposits on its bottom are greenish and white. The green- 

 ish and whitish beds of the dissected older deposits correspond to 

 these lake sediments. They represent subaqueous deposits formed 

 during the greater extent of the lake, and in continuity and uni- 

 formity, as well as color, they contrast strongly with the pink and 

 red beds formed during the contraction of the lake as subaerial 

 sediments. 



Alternating red and white layers of this type are characteristic 

 of the Moencopie formation of northern Arizona and southern 

 Utah, a deposit of Permic age. The absence of fossils and the 

 general close correspondence between these beds and the series 

 exposed in the dissected basin of Seyistan have led Huntington to the 

 conclusion that both have a similar origin. 



Alternations of gray and green sandstones with red clays are 

 well shown in the Middle Siwalik group, a late Tertiary deposit 

 exposed in the foothills of the Himalayas. As previously noted, 

 this formation represents a fluviatile deposit, of the type now form- 

 ing over the Indo-Gangetic plain. A corresponding Devonic ex- 

 ample is seen in the Catskill formation of eastern New York and 

 Pennsylvania, where, through a thickness of perhaps 5,000 feet. 



