THE BASIN PROVINCE 151 



quartz grains are also found, but the prevailing light-red to red-yellow hue of the 

 strata is maintained chiefly by the ferritic pigment which, with calcite, constitutes 

 the cement. Light-colored specks of kaolin are present in the hand specimen 

 and in places give the rock an appearance of a mixture of salt and cayenne pepper. 

 Mica and black quartz are also sparingly distributed. 



"Cross-bedding is a characteristic feature of the De Chelly sandstone. Here 

 and there the entire wall of a canyon consists of interlocking curved beds; else- 

 where massive cross-bedded strata are replaced along the strike by horizontally 

 foliated sandstones. The cross-laminae may be a foot or more in thickness, but 

 usually they measure less than an inch and in many places the division planes are 

 so closely spaced that the structure is concealed, the rock surface being completely 

 overspread by a lace-work of intricate curves. Typically the canyon walls in 

 the De Chelly sandstone are marked by sweeping curved bands 20 to 200 feet 

 long, tangential to a horizontal surface and flatly convex upward. 



"The De Chelly sandstone is traversed by wide-spaced joints which, together 

 with the curved cross-bedding foliation, allow the agents of erosion to carve 

 alcoves, recesses, and tunnels in great variety and on a scale that ranges from 

 ornamental pockets to great arched-roof alcoves in which, high on the canyon 

 walls, are tucked away single houses or whole villages of cliff dwellings. 



"Physiography of Permian Time. 



"Gilbert conceived the whole plateau country as 'covered by an inland sea 

 entirely separate from the ocean * * * from the close of the Carboniferous to 

 the beginning of the Cretaceous.' As a result of studies in the Grand Canyon 

 region Walcott reached the conclusion that — 



" ' It is probable that the era of the deposition of the Permian was one of slow 

 movement of the sea bed. Elevation and depression are indicated strongly by a 

 marked unconformity, by erosion, in the lower portion of the upper Permian. 

 * * * The sediments are mostly detrital in character, and ripple-marks and other 

 indications of a littoral deposit are also seen at several horizons.' 



"Robinson considered the Moenkopi of the San Francisco Mountain volcanic 

 area as ' fluviatile or lacustrine' in origin. Huntington and Goldthwait concluded 

 that ' the A-Ioenkopi series was probably laid down in a shallow sea where estuarine 

 conditions may possibly have prevailed.' In a later paper Huntington ascribed 

 these beds to alternate lacustrine and subaerial deposition incident to the expan- 

 sion and contraction of waters of a lake contained within an inclosed desert basin. 



"The Plateau Province during Permian (?) time was probably a region of low 

 relief bordering the sea and having an arid climate. Over the long slopes and 

 into the flat-floored depressions, sediments were carried from surrounding lands 

 and deposited on flood plains, piedmont slopes, and the floors of fresh and alkaline 

 lakes. The remarkable banding of subequal dimensions displayed in certain 

 localities and so vividly described by Dutton indicates cycles of change of roughly 

 equal. length. In some places the sediments suggest change from subaerial to 

 lacustrine deposition ; in others marine strata are interbedded with materials of 

 flood slopes. Deposits of gypsum alternating with ripple-marked beds of lenticu- 

 lar sand point to fluctuation in volume of the water contained by ephemeral lakes. 

 Ancient playas, deltas, and flood plains are suggested by rain prints, mud cracks, 

 and the almost universal presence of shining films of clay and mica and halite 

 pseudomorphs that coat the planes of foliation. The general absence of fossils, 

 other than fragments of vertebrates and xerophilous plants, is suggestive of 



