72 



C. L. DAKE 



the unconformable relations both northwest "and southeast, it 

 is highly probable that the unconformity also exists along the 

 San Juan. 



STRATIGRAPHIC MAGNITUDE OF THE UNCONFORMITY 



Stratigraphically, near Mule Twist Canyon, this unconformity 

 represents at least two hundred feet of erosion. If the beds in the 

 Mule Twist vicinity are actually different geological horizons x 



Fig. 8. — Detail of contact of sandy shale shown in Fig. 7, on Kaibab limestoile. 

 Note pebbles of limestone in the shale. 



from those near Fruita, rather than different facies of the same 

 horizon, a conclusion that seems highly probable, then the pre- 

 Moenkopi erosion was even greater. 



Let us examine now the significance of certain tentative cor- 

 relations made by Girty and presented by Woodruff.^ Regarding 

 the age of the Goodridge limestone in the San Juan Field, Girty 

 says: 



I have already examined and reported upon a collection from the Honaker 

 trail, where a good portion of Mr. Woodruff's material was obtained. This 

 collection was made by Robert Forrester, of Salt Lake City, Utah. Mr. For- 

 rester, who has done much work of a very accurate kind involving the Mesozoic 



'E. G. Woodruff, op. cit., pp. 75-164. 



