286 SMITHSONIAN MISCELLANF.OITS COLLFXTIONS VOL. 75 



Feet Meters 



la. Gray, rough-weathering magnesian limestone in layers 



6 inches (15.2 cm.) to 4 feet (1.2 m.) in thickness that 



dip to the west-southwest 35° to 40° 195 59.4 



lb. Thick-bedded, gray and rcddish-buff-weathering, rough- 

 surfaced limestones 380 1 15-9 



At 200 feet (60.9 m.) from the top, 3 or 4 thick 

 layers are covered on the upper surface with the 

 ends of large, more or less cylindrical growths of 

 Collenia^ (see fig. 28). 



ic. Massive series of light gray, thick-bedded, hard, rough- 

 weathering magnesian limestones that form the high 

 western front face of the ridge of Oyster Peak and 

 Ridge 980 298.7 



Fauna. — Only a few traces of large annelid borings and 

 trails. 



The lower strata of the Lyell form the narrow, 

 sharp ridge of Oyster Peak, east of which the sub- 

 jacent softer, arenaceous limestones and shales dis- 

 integrate into a fine talus slope that extends down to 

 the bottom of Cotton Grass Cirque. 



2(7. Reddish-brown, more or less arenaceous shales and 

 friable thin-bedded, arenaceous limestone with a few 

 thin, hard layers 190 57.9 



Fauna. — Fragments of broken-up trilobite tests. At this 

 zone in Tilted Mountain Cirque, about a mile (1.6 

 km.) south on the strike of the strata, a small collec- 

 tion was made that included recognizable cranidia of 

 Kingstonia sp. 



2h. Thin layers and beds of steel- and bluish-gray lime- 

 stone, with a few layers of oolitic limestone of varying 

 thickness 310 94.5 



Fauna. — Many fragments of trilobites in oolitic and bluish- 

 gray limestone. In the Tilted Mountain Cirque sec- 

 tion, a small fauna found at this horizon (2iw) gave 

 fragments of Conaspis and Kingstonia. 



Total Lyell formation 2,055 626.4 



Arctomys Formation 



la. Thin laj'ers and shales of arenaceous and calcareous 

 purplish, bufif, and gray beds, with partings and bands 

 of shale, all of the belt breaking down into fine, sandy 

 debris that extends down the slope to the little lake 



in the south side of the cirque 215 65.5 



Ripple marks, mud cracks, and casts of salt crystals 

 occur on the surface of the more compact layers. 

 (See Ranger Canyon section, p. 264, and Mount Bos- 

 worth section, p. 308.) 



^Smithsonian Misc. Coll., Vol. 64, No. 2, 1914, pi. 10, fig. 3; pi. 17, figs, i, 2. 



