J. 8. Diller — Bragdon Formation. 379 



Art. XLI. — The Bragdon Formation ;* by J. S. Diller. 



Introduction. — The Bragdon formation of Shasta and Trinity 

 counties, California, was named by Mr. O. II. Hersheyf and 

 regarded by him as Jurassic. The first fossils found;]; by my 

 party tended to confirm his view, but laterg upon structural 

 grounds it was referred provisionally to the lower part of the 

 Carboniferous. This called forth an article || from Mr. Hershey 

 maintaining at length his original views. Last summer other 

 fossils were discovered in the Bragdon confirming its reference 

 to the Carboniferous, and this article is intended to present 

 the evidence. 



Lithological character. — The Bragdon formation was desig- 

 nated by Mr. Hersheyl" to include an extensive series of thin- 

 bedded shales, sandstones and conglomerates lying some miles 

 north and northwest of Redding in Shasta and Trinity coun- 

 ties, California. The dark, often black, shales in strata rang- 

 ing from a foot to sixty feet in thickness alternate with thin 

 beds of sandstone and conglomerate. The sandstones are usually 

 normal although sometimes dark, hard, and flinty, like quartz- 

 ite and occasionally tufTaceous, but as Hershey says, and I 

 fully agree, " the conglomerates are the most characteristic 

 portion of the series."*"* 



They are generally composed in large part of black and gray 

 pebbles of quartz with others of sandstone, shale and lime- 

 stone. Generally they contain no igneous material, but in 

 some places it becomes abundant. By weathering, the lime- 

 stone pebbles disappear leaving holes upon the surface, thus 

 giving to the conglomerate a peculiar porous aspect. The beds 

 of conglomerate are usually less than ten feet in thickness, but 

 sometimes attain a maximum of nearly fifty feet. Quartz and 

 chert pebbles prevail in the smaller and finer beds and some- 

 times also in the larger beds where the pebbles are not over 

 half an inch in diameter. As the beds become coarser pebbles 

 of sandstone become most abundant, while those of limestone 

 also generally increase in number and size. 



The Bragdon conglomerate is most abundant along the Sacra- 

 mento River. Much of it is fine but some of it is coarse, with 

 one exception much coarser than that found elsewhere. It is 

 best exposed three-fourths of a mile above Elmore and also 



* Published by permission of the Director of the U. S. Geological Survey 



f Am. Geol., vol. xxiv, p. 39, and vol. xxvii, p. 236. 



iu. S. Geol. Survey, Bull. 196, p. 65. 



£ This Journal, vol. xv, p. 351. 



I Am. Geol. , vol. xxxiii, pp. 248 and 347. 



^| Am. Geol., xxvii, p. 236. 



**Am. Geol., vol. xxxiii, p. 252. 



