PRE-MOENKOPI UNCONFORMITY OF COLORADO PLATEAU 73 



and late Paleozoic rocks of Utah, reports that his fossils came from what was 

 called Lower Aubrey group in the reports of the Wheeler Survey, their Upper 

 Aubrey being our Kaibab limestone. The lists of fossils given by Meek as 

 representing the fauna of the upper RedwaU limestone show the same general- 

 facies as Mr. Woodruff's collection. The typical Redwall we know to be of 

 Pennsylvanian age in the upper part and Mississippian age in the lower part, 

 so that the facts at hand seem to indicate that the strata involved in Mr. Wood- 

 ruff's collection represent the upper part of the typical Redwall limestone. I 

 do not regard it as certain, however, that the marked dissimilarity of the Kaibab 

 fauna to anything which Mr. Woodruff found in his section may not be regional 

 and that by gradual modification some of his faunas may not pass into the 

 Kaibab fauna at the same geologic level. 



If Girty is right in his tentative suggestion that the Goodridge 

 is the equivalent of the Redwall, the pre-Moenkopi erosion interval 

 at once assumes greatly added significance as a stratigraphic break 

 of notable magnitude, for this would indicate the removal, or non- 

 deposition, in the San Juan Field of the Supai sandstones and shales, 

 the Coconino sandstone, and the Kaibab limestone, all of which 

 occur above the Redwall in the Grand Canyon section, the com- 

 bined thicknesses of which are not far from two thousand feet. 

 This supposition is perhaps somewhat strengthened by the facts 

 observed near Mule Twist, where the formations resemble closely 

 the Kaibab and Coconino. The fossils collected by the writer, 

 had they not been lost, might have settled this point. It is to be 

 hoped that other collections may be secured soon from that locaHty. 

 From this it would seem that the Moenkopi may be resting on 

 Kaibab limestone near Tolchico and in the Grand Canyon, on 

 RedwaU Hmestone in the San Juan Oil Field, and again on Kaibab 

 limestone and Coconino sandstone near Mule Twist Canyon. 



The foregoing is a possibility which, the writer finds, has already 

 been considered by Cross^ in explaining the fact that the Pennsyl- 

 vanian directly beneath the "Red Beds " at Moab carries a different 

 and possibly older fauna than was found by Powell and Newberry 

 below the Red Beds farther west on Colorado River. Cross says: 



There may be a stratigraphic break, due to uplift and erosion, through 

 which the Aubrey strata found by Powell and Newberry have been removed 

 at Moab, in the Sinbad Valley, and to the mountain region to the east. This 



' Whitman Cross, "Stratigraphic Results of a Reconnaissance in Western Colorado 

 and Eastern Utah," Jour. GeoL, XV (1907), pp. 634-79. 



