Schucheri — Cambrian of the Grand Canyon of Arizona. 367 



opods. These sands were constantly reworked by the 

 waves, washing the shells out of the holes and breaking 

 them into pieces. When the sandy muds were forming, 

 seaweeds (Palmophycus) were common, along with a 

 great abundance of burrowing annelids. Trailings and 

 fucoidal casts are nearly always to be seen and also the 

 vertical burrowings of worms like Arenicolites. One of 

 the most striking features of the Bright Angel formation 

 is that nearly all of the sandstones are full of glauconite. 



In spite of the fact that almost no good fossils are to 

 be had in the Bright Angel formation, yet the physical 

 phenomena show that the epeiric sea of this time must 

 have been rich in life. This is proved by the abundance 

 of fucoidal casts, trailings, and annelid burrows. Fur- 

 ther, in some of the sandstones obolid fragments teem 

 and at times their shells make up one third of a stratum. 

 When the obolid shells are prevalent, glauconite is also 

 common, and the formation of this mineral is probably 

 conditioned by the decomposition of the organic remains. 

 On the other hand, there are entire beds of glauconite up 

 to a few inches thick that are almost devoid of fossils. 

 When glauconite is very abundant, there are also apt to 

 be thin beds and even zones a few feet thick of low grade 

 iron-ore. 



Fossils of the Middle Cambrian. — -Palceophycus casts 

 are very common and well preserved at 15 feet above the 

 Tapeats sandstone, and 150 feet higher is a glauconitic 

 sandstone replete with the brachiopods Micromitra 

 (Iphidella) pannula (White) and Obolus (Westonia) 

 chuarensis. Ten feet higher occur abundantly in thin- 

 bedded sandstones Obolus zetus and rarely Obolus 

 (Westonia) themis and Lingulella acutangula. 



The most prominent horizon for fossils, consisting 

 almost entirely of obolids, is the one just mentioned 

 which occurs from 150 to 170 feet above the base of the 

 Bright Angel formation and is at the same time a general 

 level for thin-bedded sandstones. At about this same 

 general level Walcott 3 has elsewhere collected in the 

 Grand Canyon, besides those mentioned above, Obolus 

 (Westonia) euglyphus, Lingulella perattenuata, L. lineo- 

 lata, Micromitra pealei, M. crenistria, and M. superba. 



On the Bright Angel trail at 100 to 120 feet above the 



3 C. D. Walcott, TJ. S. Geol. Survey, Mon. 51, 1912. 



