THE ORIGIN OF RED BEDS 157 



member of the Salina beds), the Bedford shale (Mississippian) , and 

 the Dunkard series (Permian) of Ohio; the Lake Superior sand- 

 stone (probably Algonkian) of northern Michigan, Wisconsin, and 

 eastern Minnesota; and the Belt series (Algonkian) of Montana and 

 British Columbia. Occasional reference will be made in this paper 

 to these formations, and to Red Beds in other countries as well; but 

 this discussion applies especially to the western group, with which 

 the writer is most familiar. 



Colors of gypsum and limestone— The beds of gypsum occurring 

 in many areas of Red Beds strata are described everywhere as 

 remarkably pure and white, except where stained by a red coating 

 washed down from overlying clastic sediments. The same is true 

 of a majority of the limestones and dolomites occurring in the red 

 series, most of which are gray or drab or bluish on fresh fracture. 

 Even the famous Redwall limestone (2,500 feet thick) underlying 

 the Aubrey Red Beds of the Grand Canyon section is gray on 

 fresh fracture; 1 its surface color is due to concentration of iron oxide 

 by weathering, to wash from above, or to both of these causes. 

 Exceptions are found in limestone or dolomite bands in the lower 

 Chugwater in Wyoming, 2 and in the Minnekahta limestone 3 of the 

 Hartville quadrangle, which are characteristically purplish or rosy 

 gray; and locally in certain limestones in northern Oklahoma, 

 where they are in transition to sandstone. 4 These limestones are 

 in most localities nearly or quite barren of fossils. 



Color in clastic strata.— Another and perhaps a yet more signifi- 

 cant fact is the variation of hue among the clastic strata. Inter- 

 bedding of greenish, gray, or buff beds with red sediments is found 

 in a majority of Red Beds sections; notably in the Saliferous of the 

 Colorado and Zuni plateaus, in the Dockum group of Texas, and in 



1 G. K. Gilbert, "Geology of Portions of Nevada, Utah, California, and Arizona," 

 U.S. Geog. Surveys W. of the 100th Meridian, III (1875), 177-78. 



* Eliot Blackwelder and C. W. Tomlinson, "Field Notes on Work in Western 

 Wyoming, iqio and 191 1," unpublished; property of the United States Geological 

 Survey. 



3 W. S. T. Smith; Hartville Folio (No. 91), Geol. Atlas of the U.S., U.S. Geo!. 

 Survey, 1903. 



4 J. W. Beede, "The Neva Limestone in Northern Oklahoma," Okla. Geol. Survey 

 Bull. No. 21, 1914, p. 24. 



