394 H. W. TURNER — GEOLOGY OF MOUNT DIABLO. 



The Knoxville Beds. — These beds are, as usual, associated with the meta- 

 morphic rocks, and the previously described pre-Tertiary igneous rocks are 

 intruded in them. This statement may be taken with some reservation in 

 regard to the diabase area, which is practically a massif; but the peridotite 

 (serpentine) penetrates the Knoxville shales, forming a narrow dike a mile 

 long. 



The rocks of this age consist almost universally of dark shales with occa- 

 sional arenaceous and calcareous layers. Each calcareous layer is rather a 

 series of lenticular bodies than a continuous limestone stratum. This applies 

 to the Sierra Nevada as well, only there the limestone masses are hundreds 

 of feet in diameter. At Mount Diablo these lenticular masses do not exceed 

 twenty feet in width, measuring across the strike. It is mostly in the cal- 

 careous strata that fossils are to be found. Besides the molluscan remains, 

 they contain elasmobranch teeth and spines and numerous minute tests of 

 foramiuifera. These tests have in some cases undergone silicification. The 

 most characteristic fossil of the Knoxville beds is Aucella. The slender 

 variety, Aucella mosquensis, Von Buch, occurs, as before stated, in Bagley 

 canon, about two miles north of the main peak ; also on the eastern side of 

 the creek that heads east of Eagle point and eight-tenths of a mile northeast 

 of that peak ; also at several points in the neighborhood of the peridotite 

 dike that lies two miles west of Eagle point ; and about one-third of a mile 

 and again one mile southwestward from the summit of Black point. 



Belemmtes occurs near the northern end of this peridotite dike in lime- 

 stone, and also in a coarse sandstone just east of the limestone. In this 

 sandstone there are calcareous pebble-like nodules, the Belemnites occurring 

 in the sandstone itself. 



I observed near the mining camp of Knoxville, in Napa county, California, 

 some croppings similar to these, in which Belemnites is to be found in the 

 sandy matrix, the included limestone pebbles containing Aucella mosquensis, 

 Von Buch. 



About one-third of a mile north of the Belemnites limestone I found in a 

 single calcareous nodule Aucella, Inoceramus, and two small gasteropods. 

 This is, I think, the first time that Inoceramus has been noted in the Knox- 

 ville beds in California. 



In a limestone nodule in strata of the Knoxville group, about one and 

 seven-tenths miles southwestward from Eagle point, just north of the serpen- 

 tine dike, I collected a fragment of wood of which a thin section was made 

 and referred to Mr. F. H. Knowlton, who states that it belongs to the genus 

 Cupressinoxylon. This genus, I understand him to say, is regarded as the 

 ancestor of the sequoias. Near the fossil wood I found a specimen of Aucella 

 mosquensis. 



The dip and strike of the Knoxville strata are usually quite variable, but 

 the dip is universally great, and the strata are frequently vertical. 



