68 



SCIENCE 



[N. S. Vol. XL. No. 1019 



the Marysville Buttes. After visiting these 

 two localities the writer was inclined to the 

 belief that the lone and Tejon had been con- 

 fused in these places. Conclusive evidence has 

 recently been obtained in the type locality of 

 the lone which demonstrates that this forma- 

 tion at that place is also merely a local faciea 

 of the Tejon-Eocene. 



Turner^ recognized three lithologic mem- 

 bers in the lone at its type locality: 



(1) The lower portion, a white clay, resting 

 upon this; (2) a white or red sandstone, and 

 (3), then a light gray, clay rock. He de- 

 scribed it as follows: 



Along the western border of the metamorphic 

 roeks is a series of nearly horizontally stratified, 

 light-colored sediments, which were deposited in 

 the waters that covered the Great Valley at the 

 time the older auriferous gravels with interbedded 

 pipe-olays accumulated in the river beds of the 

 Sierra slope. This formation attains its maximum, 

 development in the area of the Jackson sheet. The 

 lower portion of the series, composed largely of 

 white clay, is well-exposed around lone, whence 

 the formation takes its name. Farther south the 

 white clays are overlain by sandstone, above which 

 is a fine-grained clay rock. The lower, white clay 

 is in places quite free from grit and is used in 

 making pottery. Other portions are sandy. The 

 formation contains iron-ore and coal seams. The 

 sandstone is used for building purposes. It is 

 usually white, but at one quarry a brick-red va- 

 riety, colored by finely disseminated hematite, is 

 obtained. At other localities it is rusty and con- 

 tains pebbles of white quartz, passing into a con- 

 glomerate. A peculiar hydrous silicate of alumina 

 occurs abundantly in the sandstone In the form of 

 cream-colored, pearly scales. 



The clay rock occurring above the sandstone is 

 light-gray, but usually more or less discolored. 

 The fracture is, as a rule, irregular and the rock 

 frequently contains minute, tubular passages. 

 Under the microscope it is seen to be composed of 

 fine particles of feldspar and fine discolored sedi- 

 ment, with occasional quartz grains. Analyses of 

 two specimens gave 59 and 72 per cent, of silica 

 and 4.8 and 1.6 per cent, of alkali. 



The succession of white clay, sandstone and clay 

 rock may not be constant throughout the entire 

 area mapped as belonging to the lone formation. 



2 Turner, H. "W., Jackson Folio, California, 

 U. S. Geol. Surv., p. 2, 1894. 



It has been suggested that the white clay of the 

 lower beds are formed from rhyolitic tuffs, in. 

 which case eruptions of rhyolite must have oc- 

 curred at the beginning of the lone epoch. 



The thickness of the lone formation is known 

 partly by natural exposures, partly by boring. In 

 Jones Butte the strata, protected from erosion by a 

 lava cap, are 200 feet thick above Coal Mine No. 

 3. A boring at the mine is said to have pene- 

 trated sandy clay to a depth of 800 feet below the 

 coal seam, which is 60 to 70 feet below the surface. 

 Thus the lone beds appear to be more than 1,000 

 feet thick at this point. 



To the east of Buena Vista Peak the series has a 

 visible thickness of 600 feet. The tableland south 

 and southwest of Buena Vista is chiefly composed 

 of the lone formation, overlain by rhyolitic and 

 andesitic tuff and Neocene shore gravels. The 

 lower clay occurs at the east base of the table- 

 land, and a patch of lone sandstone caps Waters 

 Peak, a little farther east, which haa an elevation 

 of about 900 feet. 



The relation of the sandstone to the clay rock is 

 finely exposed on the south side of the Mokelumne 

 Eiver, by the bridge north of Camanche. Here the 

 sandstone forms the lower part of the bank of the 

 river. The upper surface of the sandstone has a 

 gentle westerly dip, and a little west of the bridge 

 reaches the level of the river, which at this point 

 is about 175 feet above sea-level. East of the 

 bridge it rises at an angle of about 1°, reaching 

 an altitude of 1,000 feet on the flat ridge just 

 north of Valley Springs Peak. Along the banks 

 of the Mokelumne west of Lancha Plana this sand- 

 stone attains a thickness of more than 100 feet. 



Turner in describing the E'eocene shore 

 gravels states their relationship to the lone as 

 follows : 



The most striking evidence of nonconformity, 

 however, may be seen at the red sandstone quarry 

 three miles southeast of Buena Vista. Here the 

 Neocene shore gravels rest unconformably on the 

 smooth, waterworn surface of the sandstone, which 

 is red where quarried, but white at the northern 

 end of the exposure. Waterworn bowlders of the 

 white sandstone may be seen in the gravel. South- 

 west of the quarry the ridge is capped for a dis- 

 tance of more than a mile with the same gravel, 

 which half a mile from the quarry contains a layer 

 of andesitic detritus. At the extreme southwest- 

 ern end of the ridge is a body of similar gravel, 

 which also rests plainly on sandstone of the lone 

 formation. 



