THE BASIN PROVINCE 



137 



dillera of the United States a few areas show the condition during the upper- 

 most Pennsylvanian time. 



In California two formations have been recognized as Pennsylvanian 

 Robinson and Calaveras. 



The Robinson formation is described by Turner 1 as "sediments and 

 trachyte tuffs," with fossils of upper Carboniferous age, and by Diller 2 

 as containing shales, conglomerate, tuff, and sandstone, of which the last 

 two are the most important. The sandstone is a purplish rock of great 

 variability. One-fourth of a mile south 50 west of Robinson's, in Genesee 

 Valley, it becomes for a short distance an arenaceous limestone. 



J. P. Smith 3 considers this as equivalent to the Carboniferous portion 

 of the Pitt formation of Shasta County. 



In northern California, north of the fortieth parallel, the upper Penn- 

 sylvanian is represented by the McCloud limestone and the Pitt shales. 

 Smith 4 gives the following table of the formations of Shasta County: 



The McCloud shales are correlated with the Robinson formation, and 

 both have been separated off as the Nosoni formation. 



The. McCloud limestone is described by Diller* as a dark gray sand, 

 massive below and lighter colored and somewhat thinner above, with many 

 nodules of chert and sheets of gray chert, often containing silicified fossils. 



The McCloud limestone, according to J. P. Smith, 6 is about 



"2,000 feet in thickness, uniform in bedding, and very siliceous in places. Some 

 few beds are altered to a crystalline marble, but in the main the series is made 

 up of a fine-grained hard gray limestone. * * * The McCloud limestone is 

 probably equivalent to the Caribou formation of Plumas county. But J. S. 

 Diller thinks they belong to a lower horizon than that assigned them by the 

 writer. The Robinson beds of the Taylorville section are probably higher up 

 in the section, but nevertheless the McCloud limestone is, in part at least, 

 equivalent to the Coal Measures." 



1 Turner, H. \V., Bidwell Bar Folio, No. 43, U. S. Geological Survey, 1898. 

 J Diller, J. S., Geology of the Taylorsville Region, California, Bull. Geol. Soc. Amer., 

 vol. 3, p. 374, 1892. 



* Smith, J. P., The Metamorphic Series of Shasta County, California, Jour. Geol., vol. 2, 



p. 602, 1894. 

 'Idem. 



* Diller, J. S., Redding Folio, No. 138, U. S. Geological Survey, 1906. 



* Smith, J. P., The Metamorphic Series of Shasta County, California, Jour. Geol., vol. 2, 



pp. 599 and 601, 1894. 



