on the Navajo Reservation. 105 



stone carrying Productus cor a, Spirifer rocky montanus, 

 Pugnax Utah, and other characteristic Pennsylvanian fossils 

 are identical with the strata of the Goodridge formation found 

 in the San Juan Canyon, at a stratigraphic horizon several 

 hundred feet lower than their position at Mule Ear. The 

 igneous and metamorphic fragments are from a much greater 

 depth. 



The Moses Rock Field. 



One of the sources of the " Arizona rubies " (pyrope garnets), 

 offered to traders by the Navajo Indians, is a broken line of 

 rounded knobs about two miles west of Moses Rock, Dtah, 

 In this region, — an area which has a north-south extension of 

 about six miles and a width varying from less than five feet to 

 one and one-half miles, — the bed rock is mantled by drift made 

 up of fragments of granite, basic igneous rocks, a variety of 

 gneisses, schists, and slates, and blocks of limestone and sand- 

 stone. On the west the field has a somewhat definite border ; 

 on the east the erratics are distributed along the water courses 

 or in mesas and ridges and mounds in an apparently capricious 

 manner. In the canyons northwest of Moses Rock the erratics, 

 at first sparingly distributed on the dry valley floors or dis- 

 played on intercanyon mesas, increase in abundance westward 

 to the crest of the ridge whose rounded and broken summit is 

 buried in gravels, cobbles and bowlders, and square blocks 

 from one inch to three feet in diameter. On the extreme sum- 

 mit of the ridge blocks of limestone 10 to 20 feet in width are 

 mingled with the finer materials. A reconnaissance of the 

 field indicated that the erratics were concentrated along a nar- 

 row irregular band with an average north-south trend and that 

 the bowlders strewn over the eastern portion of the field owe 

 their position to the storm water torrents which add their floods 

 to the Chinle. The " drift "-covered belt consists of three dis- 

 tinct portions : 



1. The northern portion, two miles in length, is a band 2-5 

 feet in width, consisting of an agglomerate of buff limestone 

 and sandstone containing Pennsylvanian fossils. Included 

 within this mass are fragments of red shale, sandstone, quartz- 

 ite. minette, granite, and gneiss. Viewed from a distance this 

 belt appears as a yellow-green streak crossing canyon and flat 

 and ridge, sharply outlined against the dark red sandstone and 

 shales of the Moenkopi formation. Its trend is _N~. 10° W., 

 but numerous offsets of 10-50 feet give to the line a zigzag 

 form. This conglomerate band is even with the surface 

 throughout most of its extent, but on canyon walls it is re- 

 placed by a trench and at a few places it stands above the sur- 

 face as the core of small mesas. The band clearly cuts the 



