Paleozoic Groups of Arizona. 223 
reddish-brown gypsiferous marl that becomes more arenaceous 
below, finally passing into a sandstone that rests on the choco- 
ate and cream-colored limestone Dene This kee suffered 
Ba es is a sue i the Upper Aubry group. A hes plane 
of erosion with an ene change in the character of the rock 
separates the two g 
The Permo- OP ie of Mr. G. K. Gilbert* is the same 
as my lower division of the Permian. It is placed as a subdi- 
vision of the group, now that the beds above are known to be 
of Permian age. 
The stratigraphy of the section shows a group separable into 
two divisions, defined above and below by planes of unconform- 
ity by erosion and a decided change in the character -of the 
es from those of the subjacent and superjacent formations. 
There is no physical break in the beds above the Permian lime- 
stone of the upper division before the conglomerate is reached. 
This stratigraphical arrangement is sustained by the evidence 
of the fauna found in the limestones and associated arenaceous 
layers in the upper division. 
“The genera Myalina, Schizodus, Nucula, Aviculopecten, Murchi- 
sonia, Naticopsis and Goniatites are represented in the lower 
chocolate-colored limestone. The fauna is distinct in specific 
character from that of the Carboniferous groups beneath, oe 
more intimately related to that of the fossiliferous beds of t 
pper Permian division. Mr. G. K. Gilbert obtained from ce 
same horizon Pleur oto Schizodus and Bakevellia a group 
of shells, as he states, suggesting the Permo-carboniferous of the 
Mississippi Valley.t 
Twenty-three genera  Teprenenies by wut four species com- 
prise el fauna of the upper division. Of these the basa 
have strong Paleozoic relations: Scolithus ——?, Lingula my 
andes Discina nitida, Orthis ?, Rhynchonella Uta, pe eee 
» Nucula, 2 species, Aviculopecten, 3 species, Myalina, 4 
ne Nulconea.. 2 species, Pleurotomaria ——?, ‘Maer ocheilus 
?, Cyrtoceras ?, Gontatites ?, and Nautilus 2. 
The Permian character of the fauna is more marked by the 
presence of Plewrophorus, 8 species, Schizodus ?, 3 species 
of Bakevellia including B. parva, Pteria tilus ?, 
Uss00 ?, and the still more gene Mesozoic genera Pen- 
2. 
tacrinus and Pi ‘Lleol 
e Pentacrinus plates were discovered by Mr. Edwin E. 
* Wheeler Survey, West of the Borg sce iii, p. 177, 1875. Also, see 
Arch. R. agit d s Report in same, 
+ Ibid. ep p. 2 
