the Muddy Mountains, Nevada, etc. 



^9 



fauna of the San Andreas limestone in the Manzano 

 Group of New Mexico. 



Mesozoic Formations. 



Interval between eras. — A distinct disconformity sep- 

 arates the Kaibab limestone from Mesozoic sediments. 

 Local depressions or valleys 50 to 100 feet deep, cut into 

 the Kaibab in early Triassic or pre-Triassic time, are 

 filled with chert and limestone fragments from the under- 

 lying rock. No angular divergence was found between 

 Paleozoic and Mesozoic formations. 



Fig. 4. — ''Magnesite" of the Horse Spring formation, in Muddy Valley. 

 Beds dip 32° N.E. Thickness of 300 feet shown. in figure. 



Triassic System. — The lower Triassic is represented 

 by thin-bedded limestone, shale, and sandstone forming a 

 total thickness ranging from 1,200 to 1,600 feet. In the 

 Muddy Mountains limestone makes up practically half of 

 the thickness. Typically the layers are regular, but are 

 very thin, beds more than a foot thick being exceptional. 

 Shale, sandstone, and gypsum members occur at inter- 

 vals, and abundant ripple-marks indicate shallow water 

 during deposition. Marine fossils, dominantly pelecy- 

 pods, are found at many horizons. The upper part of the 

 deposits are continental, and consist mainly of shale, 

 with abundant gypsum. Tracks of small reptiles occur 

 in the shales. 



Am. Jour. Sci.— Fifth Series, Vol. I, No. 1.— January. 1921. 

 4 



