104 Gregory — Igneous Origin of the " Glacial Deposits" 



was noted and angular blocks of Carboniferous limestone 20 to 

 100 feet in long diameter are not uncommon. This accumula- 

 tion of igneous and metamorphic rock appears strangely out of 

 place since no materials of these types are found in situ within 

 the limits of the Navajo Reservation or beyond its borders for 

 a distance of 100 miles from Mule Ear. 



Among the materials capping the ridge masses of conglom- 

 erate, consisting of the materials represented in the " drift," 

 were noted, and where outcrops are favorably displayed lenses 

 and stringers of this conglomerate appear wedged between the 

 blocks and tightly plastered against limestone and sandstone 

 fragments. At the immediate contact between the conglom- 

 erate and the sedimentary rock, the limestone is in places dis- 

 colored and partially crystallized and the sandstone is baked or 

 even altered to a vitreous quartzite. In the jumbled mass it 

 was found impracticable, with the time at our disposal, to map 

 the scattered outcrops or to determine their inter-relations. 

 Across the top of the ridge dark green bands of decomposed 

 rock were noted, which on examination proved to be composed 

 of fragments of igneous, metamorphic, and sedimentary rock 

 set in a groundmass of finer materials. These bands, 2 to 6 

 feet wide, intersect the strata at various angles, have distinct 

 borders, and are sharply differentiated from other portions of 

 the terrane by their color. At no point was the material com- 

 posing these streaks consolidated at the surface or in the two- 

 foot trenches dug to determine their character. On the east 

 side of the ridge one of these bands, traversing the strata in a 

 vertical direction, was found to consist of fragments of granite, 

 gneiss, schist, quartzite, and limestone held together by a paste 

 of basic igneous fragments. 



It will be seen from the above description that the conglomer- 

 ate is intrusive in origin and that the green bands intersect- 

 ing the upturned Mesozoic sediments are dikes of somewhat 

 unusual aspect. The material exposed is rather a heterogeneous 

 mass of sedimentary fragments intersected by stringers and 

 lenses of conglomerate and paste rather than an igneous intru- 

 sion carrying inclusions of foreign rock. The number of dikes 

 and their mutual relations was not determined, but the field 

 relations suggest a plexus of contemporaneous dikes associated 

 in a general intrusion. It is possible that the intrusion par- 

 takes of the nature of a volcanic neck or pipe, and that blocks 

 of deep-seated rock were carried upward along a poorly-den'ned 

 vent. The fact that some of the bowlders of limestone are of 

 greater diameter than the width of any of the dikes observed is 

 in harmony with this assumption. 



All the erratics of the Mule Ear field may be accounted for 

 on the assumption of igneous intrusion. The blocks of lime- 



