THE CARBONIFEROUS FAUNA. 375 



associated. In some cases it can be distinguished from the porphyritic 

 eruptive only by the presence of fossils. 



The following is a list of the forms identified by Mr. Walcott* from 

 the calcareous and tufaceous portions of the Robinson beds at the above 

 localities : 



Campophyllum (f). Streptorhynchus crenistria. 



Favosites. Productus semin ticulatus. 



Archseocidaris. Crinoids. 



Fenestella, 2 sp. undet. Productus punctatus ( ?). 



Spirifera lineata. Meekella, like striaio-costata, Cox. 



Spirifera camerata. Rhynchonella, sp. undet. 



Aviculopecten, 2 sp. ■ Aviculopecten inter lineatus. 



Myalina, of subquadrata type. Edmondia, sp. undet. 

 Pleurotomaria, sp. (?). 



Microscopic markings of Favosites have been found common in the 

 sandstone and can he used occasionally in identifying it when all other 

 fossils fail. 



IAthostrotion is an abundant and characteristic form in the Carbon- 

 iferous limestone at a number of points northwest of the Taylorville 

 region. The absence of this form among the Carboniferous fossils of 

 Genesee valley led me to suspect that there are two fossiliferous horizons 

 in the Carboniferous of northern California, of which the limestone con- 

 taining IAthostrotion is the older and the Robinson beds of Genesee 

 the younger. In answer to my .pustion. Mr. Walcott replied that " Two 

 horizons appear to be represented in the Carboniferous fauna. The 

 Lower is at the locality west of Bass ranch, near Pit river: also south 

 of Longville, on crest of Mosquito and Yellow creeks. A somewhat 

 higher zone is indicated by the collection from southwest of Robinson's, 

 Genesee valley, and the Little Grizzly locality on the Cascade Gravel 

 Mine road, in Plumas county. The collections do not clearly define the 

 lower and upper Carboniferous zones of the Mississippi valley, but they 

 suggesl t rial they are present." 



The Shoo Fly beds include a lime-tone which crops out on Clear creek . 

 about two miles southeast of Shoo Fly bridge. It contains traces of 

 crinoid stems, but they are not sufficient to determine positively whether 

 the limestone is Paleozoic or Mesozoic. On structural grounds, it is 

 probably either Triassic or Carboniferous, perhaps with a sligh.1 presump- 

 tion in favor of the hitter. 



The Arlington beds, which form Hough peak and Arlington heights, 



* Reporl rendered I >< ceml 



