PENNSYLVANIC-PEKMIC PERIOD 573 



foraminifer Schwagerina and the corals Clisiophyllum gdbhi, Lonsdalia 

 sublcevis, L. calif or niense, Syringopora multattenuata ?, Hustedia com- 

 pressa, etcetera. Girty 212 correlates this formation with "the lower por- 

 tion of the Hueco." The latter "will perhaps prove to be the same as the 

 Aubrey formation of northern Arizona," both of which are regarded as of 

 late Pennsylvanic age. This horizon also appears in Alaska and the Arc- 

 tic regions, being here marked by Spiriferella arctica. When these strange 

 faunas were first seen by the writer, 213 particularly because of the variety 

 of the Producti, he regarded their age as Permic. It is now known that 

 they correlate best with the Omphalotrochus and higher Pennsylvanic 

 faunas of California and Eussia. The writer was first impressed with 

 this resemblance while on a visit to the Geological Survey collection at 

 Saint Petersburg, in 1903, and he still regards the Alaskan faunas as best 

 compared with the Omphalotrochus and Pro ductus cor a zones of Eussia. 



The McCloud limestone is succeeded by the McCloud shale, or Nosoni 

 formation, "composed very largely of andesite or basalt tuffs and tuffa- 

 ceous conglomerates and a few flows of lava, but locally interstratified 

 with these volcanic products are shales and sandstones, in part calcareous, 

 and often rich in fossils." The thickness varies between 500 and 1,200 

 feet. On Little Grizzly creek, Plumas county, occur Fusulina elongata, 

 Chonetes (a large new form), Marginifera longispina, Rhipodomella pe- 

 cosi, Pugnax utah ?, Uncinulus cf. theooaldi, Meehella cf. striaticostata, 

 Spirifer much lij^e camerata and musaklneylensis. Girty states that the 

 ""McCloud shale may provisionally be correlated with the upper Hueco- 

 nian." It also seems to correlate with the Schwagerina zone of the 

 Eussian geologists. This zone is just below the Permo-Carboniferous or 

 Artinskian. 



Hueconian (Pennsylvanic) of the Trans-Pecos region of Texas. — In 

 this part of Texas there is no equivalent of the Pottsvillian, the Hueconian 

 apparently representing the Upper Missourian of the Cordilleran region. 

 The Hueco formation consists of a massive limestone with zones of shale 

 and sandstones, ranging in thickness from 3,000 to 5,000 feet. The fauna 

 found at the base is somewhat similar to that of the late Pottsvillian, but 

 the higher assemblages are quite different from those of the Pennsylvanic 

 of the Mississippi valley and are mostly undescribed. "Through the 

 West, however, these faunas will probably prove to have extended widely." 

 The Hueco "will perhaps prove to be the same as the Aubrey formation of 

 northern Arizona" (Girty, 1905, 14). 



313 Girty : Proceedings of the Washington Academy of Sciences, vol. 7, 1905, p. 16. 

 213 Schuchert in Mendenhall : Professional Paper no. 41, U. S. Geological Survey, 1905, 

 pp. 42-45 ; also Kindle, Journal of Geology, 1907. 



