152 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



continental conditions. Aridity is suggested by the presence of feldspars and 

 by the prevailing reds and browns of the rock, which are inconsistent with the 

 presence of ground water near the surface. The cross-bedding also points to 

 aridity, for while angular cross-bedding of types common on alluvial plains and 

 even on the seashore occurs in many strata, tangential cross-bedding of the eolian 

 type is prevalent. 



"Toward the end of the Permian epoch aridity reached a stage where sand 

 dunes became a prominent feature. These are best preserved along the east 

 and northeast sides of the area, where the De Chelly sandstone displays the record 

 of wind work during late Permian (?) time. The walls of Canyon de Chelly 

 consist in part of overlapping heaps of wind-blown sand now weakly cemented 

 into rock. In the picturesque Navajo language they are 'frozen dunes.' 



"The exact sequence of events during Permian (?) time has not yet been made 

 out, but the final explanation must allow for extensive subaerial sedimentation 

 under arid conditions and for two or more invasions of the sea. It is not neces- 

 sary, however, to assume that all parts of the great area in which Permian 

 deposits occur had the same physiographic history." 



In a recent paper upon the Carboniferous of the Grand Canyon, 

 Schuchert 1 has suggested that the Kaibab limestones, the Coconino sand- 

 stone and even the upper part of the Supai formation are Permian. He says : 



"That the Kaibab limestone is of early Permian age is now admitted by most 

 American stratigraphers. This view, however, has been attained rather from 

 its field relations than through a study of its marine fossils, for these in several 

 forms are very much like those of the Pennsylvanian. The fauna as collected 

 by Noble in the Shinumo quadrangle is listed by Girty and he here correlates 

 the Kaibab limestone with the Manzano group of New Mexico. He also suggests 

 that the Kaibab may be equivalent to a part of the Guadalupian of southwestern 

 Texas, a formation of undoubtedly Permian age." 



The remarks made by Girty scarcely seem to convey to the author so 

 definite an idea of the Permian age of the Kaibab as is received from them 

 by Schuchert. Girty says in a letter to Noble 2 concerning the fauna collected 

 from the Kaibab: 



"The list is typical of the fauna of the upper Aubrey, the general character 

 of which has long been known through similar lists made up by Meek and others. 

 I have been tentatively correlating the Aubrey with the Manzano of New Mexico 

 and with the upper part of the Hueco formation of western Texas. Consequently, 

 it would be older than the Guadalupe group, which overlies the Hueco formation. 

 The fauna listed above, however, contains a number of species which are very 

 similar to or identical with species which occur in the Guadalupian fauna, and 

 in spite of the fact that most of the Guadalupian species have not been found in 

 the Aubrey group, it seems less improbable than it did several years ago, when the 

 Guadalupian fauna was under investigation, that the Kaibab limestone is of the 

 same geologic age." 



1 Schuchert, Chas., On the Carboniferous of the Grand Canyon of Arizona, Amer. Jour. 



Science, vol. XLV, p. 347, 1918. 



2 Girty, in L. F. Noble, The Shinumo Quadrangle, U. S. Geological Survey Bull. 549, 



p. 71, 1914. 



