520 INDEX TO THE STRATIGKAPHY OF NORTH AMERICA. 



"Cedar formation," comprising the Swearinger slate and Hosselkus limestone. 

 Smith ^'^^'^ says: 



The Cedar formation was first named by J. S. Diller » to include the Upper Triassic slates 

 and limestones of Indian Valley, Plumas County, and Cedar Creek, Shasta County. It there- 

 fore includes the original Trias described by Gabb '' from "Giflford's ranch." 



In the Pitt River region the formation is very similar to that in Plumas County, being 

 composed of finely laminated shales overlain by massive limestone, each rich in fossUs. It 

 seems to overlie conformably the siliceous shales of the Pitt formation, but the contact could 

 not be observed. 



The Triassic of Plumas County, Cal., has been discussed by Diller ^" and 

 Hyatt .^"^ In a recent publication on the geology of the Taylors ville region Diller ^^"' 

 gives the following section : 



Triassic : 



Unconformity. Feet. 



Swearinger slate: Dark slaty calcareous shales, with thin limestones and some siliceous beds. 200 



Hosselkus limestone: Dark-blue to light-gray limestone 140 



Unconformity. 



The Hosselkus limestone is dark blue on fresh fracture but weathers light gray. * * * 

 It is thin bedded and in some places decidedly slaty * * * and characterized by small 

 ammonites. * * * j^ ^jjg Redding region * * * the upper part is hghter colored and 

 more massive, with a Spirifer-like shell, and the lower part thinner bedded and darker, with 

 small coiled forms. 



The fossils collected from this limestone by Prof. Hyatt and others in the Taylorsville 

 region have not yet been fully worked up. A partial list is given by Hyatt: " 

 I. Arcestes, phylum of A. tomati. 

 Arcestes, phylum of A. galeati. 

 Arcestes, phylum of A. bicarinati. 

 Arcestes, phylum of A. sublabiati. 

 Badiolites, allied to B. eryx Mojsisovics. 

 Juvavites, allied to J. erlichi Mojsisovics. 

 Tropites, may be young of species occurring in Halobia slates. 

 Atractitea. 



"Arcestes (I) is very abundant, but whether the other forms are abundant or not it is 

 difScult to say at present. The materials gathered show that the rock is full of fossils, but 

 these can not be obtained in any reasonable time by means of surface work. Besides the 

 species mentioned, there is a form of Acrochordiceras, with finer costse than those occurriag 

 ia the Muschelkalk, a possible Balatonites, like B. waageni of the Noric, and some other frag- 

 ments of Ceratitinse, all indicating a fauna rich in ammonoids, which will some day yield a 

 good harvest to patient work." 



Prof. Hyatt concludes that the age of the Hosselkus limestone as indicated by the fossils 

 is upper Triassic. To this list Spiriferiaa and fish vertebra, as determined by Stanton, were 

 added last summer. This limestone has not yet been thoroughly examined for reptilian remains, 

 such as J. C. Merriam has found in the Redding quadrangle, but as the limestone of the Taylors- 

 ville region is more altered and much less fossiliferous, reptilian remains are less likely to occur. 

 In the Redding region the more massive upper portion of the Hosselkus limestone is char- 

 acterized by the presence of Spiriferina, while the lower, darker, thin-bedded portion often 

 abounds in small ammonites. * * * 



The reference of the Hosselkus limestone to the upper Triassic and the Robinson formation 

 to the upper Carboniferous indicates a decided gap between them, a gap which is at least 

 partially filled in the more complete section of the Redding region, where a great thickness 



' = Lassen Peak folio (No. 15), Geol. Atlas U. S., U. S. Geol. Survey, 1895. 

 6 Paleontology of California, vol. 1. 

 c Bull. Geol. Soc. America, vol. 3, 1892, pp. 399-400. 



