. BEDS OF THE ELDER CREEK SECTION. 441 



stones are most abundant in the lower half of the Knoxville ; in the 

 upper half they are unconinion. Both north and south of Elder creek 

 the Knoxville beds contain thick strata of conglomerate which do not 

 appear in the measured section. The base of the section is serpentine, 

 which has resulted from the alteration of an eruptive rock, in all proba- 

 bility belonging to the peridotites.* Ripple marks have been found in 

 this portion of the section showing that the rocks were deposited in 

 shallow water. 



The shales of the Knoxville beds, with occasional thin layers of sand- 

 stone, continue upward Avithout any interruption either in the character 

 of the sediments or in the position of the strata, into the Horsetown beds. 

 On account of the gradual transition in all respects from the Knoxville 

 to the Horsetown beds it is impossible to draw a sharp line between 

 them. Aucella being the most abundant, widely distributed and char- 

 acteristic fossil of the Knoxville beds, it seems best to draw the line upon 

 a paleontological basis at the upper limits of the Aucella-henYmg layers. 

 At that horizon fossils are usually abundant. 



The Horsetown beds in this section are composed chiefly of shales, 

 although there are some sandstones of considerable size. One was ob- 

 served 50 feet in thickness, another 12 and a third 8 feet. Few fossils 

 were found in these beds along Elder creek, but a short distance to the 

 southward in the Bald hills, innnediately above the Knoxville, the}^ are 

 more fossiliferous and contain the Horsetown species mentioned on page 

 446. Several miles east of Lowreys, on Elder creek, the basal portion of 

 the Chico is rich in fossils. Here is found an intermingling of numerous 

 Chico and Horsetown forms. 



The Chico, which has a thickness of nearly 4,000 feet in this section, 

 is composed chiefly of sandstones and conglomerates. The basal portion 

 is made up of conglomerates altogether. The upper portion for 1.100 

 feet is composed chiefly of shales, and there are some shales lower down 

 intercalated between the sandstones and conglomerates. The conglom- 

 erates at the base contain numerous nodules of limestone which are rich 

 in fossils. Here was found Coralliochama orcutti, the characteristic Wal- 

 lala fossil, in exactly the position predicted for it by Dr White. Its 

 occurrence in the basal portion of the Chico of this section, as well as 

 others upon the western border of the Sacramento valley with a large 

 number of Chico fossils, completely demonstrates, as already urged, that 

 the AN'allala beds are only a phase of the Chico. 



*A lew miles soutlivvest of Paskenta, by the road to Round vallej', a large dike of serpentine 

 a(«pears to cut directly across the Knoxville beds, and thei-e can be but little, if any, doubt, as 

 shown also by Fairbanks (American Geologist, March, 189-2) and Turner (Bull. Geol. Soe. Am., vol. 

 2, pp. 318-402), that the serpentine of the Coast range are altered eruptive rocks younger than the 

 Knoxville portion of the Shasta-Chico series. 



