SMITHSONIAN EXPLORATIONS, I93O 27 



where it cuts across this block, has the usual steep canyon, but up- 

 stream it widens into a basin where softer rocks have been removed. 

 Doctor Walcott's interpretation of this unorthodox fault is sometimes 

 questioned, but Doctor Stoyanow and I, after considerable discussion 

 of several alternatives, think Doctor Walcott is correct ; in fact, we 

 found further corroborative evidence not mentioned in his publica- 

 tions. 



Our chief task on this expedition was to search the rocks thoroughly 

 for traces of animal remains. As expected we found abundant im- 

 prints of delicate plant tissues and rather large masses of algal lime- 

 stones, but nothing that can really be regarded as animal, though the 

 limey and carbonaceous shales are fitted in every way to preserve a 

 record of the life extant in the waters by which the sediments were 

 deposited. Just what significance the barrenness of these sediments 

 has, is not yet apparent. We camped, without tents, in the channel of 

 Nankoweap Creek under a cutbank where one of the half-dozen siz- 

 able trees in the basin is located at the only campsite in the valley near 

 water. Each day the search for fossils was extended to new ground 

 so that almost every exposed bed was investigated in the eight days we 

 remained in this basin. 



When we prepared to climb out of the Nankoweap basin, I did not 

 care to trust my notes or photographs to the mule but carried them in 

 my pack. Fourteen hours of strenuous work were required to climb the 

 vertical mile between our camp and the north rim, and to traverse the 

 15 miles of trail to the point on the road where the Park Service auto- 

 mobile could pick us up. Within the Canyon the last few days had 

 become quite hot, but on the north rim we found early spring, with 

 the snow bank just shoveled from the hotel porch and spread in the 

 sun for quicker melting. The crossing to the South Rim, which was 

 completed in a snow storm, seemed very cold, since we were outfitted 

 for the heat of the canyon depths. 



Now that the Nankoweap trip was completed, Doctor Stoyanow 

 kindly arranged for use of the State Geological Survey automobile 

 to afford us means for a brief examination of other Arizona Cambrian 

 outcrops. This interesting journey began with the study of the Music 

 Mountain section west of Peach Springs. A day here showed us how 

 this section, which offhand would be assumed to coincide exactly with 

 its apparent continuation northward in the Grand Canyon, differs in 

 lithologic detail and relative thickness of beds. From Peach Springs 

 our course naturally led southeastward diagonally across the State, for 

 the older strata outcrop only along the northeastern edge of the old 

 basement rock mass forming the southwestern portion of the State. 



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